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This has a number of shortcomings. First, this imposes atomic requirements on compression backends. zram can call both zcomp_compress() and zcomp_decompress() under entry spin-lock, which implies that we can use only compression algorithms that don't schedule/sleep/wait during compression and decompression. This, for instance, makes it impossible to use some of the ASYNC compression algorithms (H/W compression, etc.) implementations. Second, this can potentially trigger watchdogs. For example, entry re-compression with secondary algorithms is performed under entry spin-lock. Given that we chain secondary compression algorithms and that some of them can be configured for best compression ratio (and worst compression speed) zram can stay under spin-lock for quite some time. Having a per-entry mutex (or, for instance, a rw-semaphore) significantly increases sizeof() of each entry and hence the meta table. Therefore entry locking returns back to bit locking, as before, however, this time also preempt-rt friendly, because if waits-on-bit instead of spinning-on-bit. Lock owners are also now permitted to schedule, which is a first step on the path of making zram non-atomic. Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zram_drv.c | 62 ++++++++++++++++++++++++++++------- drivers/block/zram/zram_drv.h | 20 +++++++---- 2 files changed, 65 insertions(+), 17 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 9f5020b077c5..37c5651305c2 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -58,19 +58,62 @@ static void zram_free_page(struct zram *zram, size_t in= dex); static int zram_read_from_zspool(struct zram *zram, struct page *page, u32 index); =20 -static int zram_slot_trylock(struct zram *zram, u32 index) +#ifdef CONFIG_DEBUG_LOCK_ALLOC +#define slot_dep_map(zram, index) (&(zram)->table[(index)].dep_map) +#define zram_lock_class(zram) (&(zram)->lock_class) +#else +#define slot_dep_map(zram, index) NULL +#define zram_lock_class(zram) NULL +#endif + +static void zram_slot_lock_init(struct zram *zram, u32 index) { - return spin_trylock(&zram->table[index].lock); + lockdep_init_map(slot_dep_map(zram, index), + "zram->table[index].lock", + zram_lock_class(zram), 0); +} + +/* + * entry locking rules: + * + * 1) Lock is exclusive + * + * 2) lock() function can sleep waiting for the lock + * + * 3) Lock owner can sleep + * + * 4) Use TRY lock variant when in atomic context + * - must check return value and handle locking failers + */ +static __must_check bool zram_slot_trylock(struct zram *zram, u32 index) +{ + unsigned long *lock =3D &zram->table[index].flags; + + if (!test_and_set_bit_lock(ZRAM_ENTRY_LOCK, lock)) { + mutex_acquire(slot_dep_map(zram, index), 0, 1, _RET_IP_); + lock_acquired(slot_dep_map(zram, index), _RET_IP_); + return true; + } + + lock_contended(slot_dep_map(zram, index), _RET_IP_); + return false; } =20 static void zram_slot_lock(struct zram *zram, u32 index) { - spin_lock(&zram->table[index].lock); + unsigned long *lock =3D &zram->table[index].flags; + + mutex_acquire(slot_dep_map(zram, index), 0, 0, _RET_IP_); + wait_on_bit_lock(lock, ZRAM_ENTRY_LOCK, TASK_UNINTERRUPTIBLE); + lock_acquired(slot_dep_map(zram, index), _RET_IP_); } =20 static void zram_slot_unlock(struct zram *zram, u32 index) { - spin_unlock(&zram->table[index].lock); + unsigned long *lock =3D &zram->table[index].flags; + + mutex_release(slot_dep_map(zram, index), _RET_IP_); + clear_and_wake_up_bit(ZRAM_ENTRY_LOCK, lock); } =20 static inline bool init_done(struct zram *zram) @@ -93,7 +136,6 @@ static void zram_set_handle(struct zram *zram, u32 index= , unsigned long handle) zram->table[index].handle =3D handle; } =20 -/* flag operations require table entry bit_spin_lock() being held */ static bool zram_test_flag(struct zram *zram, u32 index, enum zram_pageflags flag) { @@ -1473,15 +1515,11 @@ static bool zram_meta_alloc(struct zram *zram, u64 = disksize) huge_class_size =3D zs_huge_class_size(zram->mem_pool); =20 for (index =3D 0; index < num_pages; index++) - spin_lock_init(&zram->table[index].lock); + zram_slot_lock_init(zram, index); + return true; } =20 -/* - * To protect concurrent access to the same index entry, - * caller should hold this table index entry's bit_spinlock to - * indicate this index entry is accessing. - */ static void zram_free_page(struct zram *zram, size_t index) { unsigned long handle; @@ -2625,6 +2663,7 @@ static int zram_add(void) if (ret) goto out_cleanup_disk; =20 + lockdep_register_key(zram_lock_class(zram)); zram_debugfs_register(zram); pr_info("Added device: %s\n", zram->disk->disk_name); return device_id; @@ -2653,6 +2692,7 @@ static int zram_remove(struct zram *zram) zram->claim =3D true; mutex_unlock(&zram->disk->open_mutex); =20 + lockdep_unregister_key(zram_lock_class(zram)); zram_debugfs_unregister(zram); =20 if (claimed) { diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h index db78d7c01b9a..794c9234e627 100644 --- a/drivers/block/zram/zram_drv.h +++ b/drivers/block/zram/zram_drv.h @@ -28,7 +28,6 @@ #define ZRAM_SECTOR_PER_LOGICAL_BLOCK \ (1 << (ZRAM_LOGICAL_BLOCK_SHIFT - SECTOR_SHIFT)) =20 - /* * ZRAM is mainly used for memory efficiency so we want to keep memory * footprint small and thus squeeze size and zram pageflags into a flags @@ -46,6 +45,7 @@ /* Flags for zram pages (table[page_no].flags) */ enum zram_pageflags { ZRAM_SAME =3D ZRAM_FLAG_SHIFT, /* Page consists the same element */ + ZRAM_ENTRY_LOCK, /* entry access lock bit */ ZRAM_WB, /* page is stored on backing_device */ ZRAM_PP_SLOT, /* Selected for post-processing */ ZRAM_HUGE, /* Incompressible page */ @@ -58,13 +58,18 @@ enum zram_pageflags { __NR_ZRAM_PAGEFLAGS, }; =20 -/*-- Data structures */ - -/* Allocated for each disk page */ +/* + * Allocated for each disk page. 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charset="utf-8" Currently, per-CPU stream access is done from a non-preemptible (atomic) section, which imposes the same atomicity requirements on compression backends as entry spin-lock, and makes it impossible to use algorithms that can schedule/wait/sleep during compression and decompression. Switch to preemptible per-CPU model, similar to the one used in zswap. Instead of a per-CPU local lock, each stream carries a mutex which is locked throughout entire time zram uses it for compression or decompression, so that cpu-dead event waits for zram to stop using a particular per-CPU stream and release it. Suggested-by: Yosry Ahmed Reviewed-by: Yosry Ahmed Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zcomp.c | 41 +++++++++++++++++++++++++---------- drivers/block/zram/zcomp.h | 6 ++--- drivers/block/zram/zram_drv.c | 20 ++++++++--------- 3 files changed, 42 insertions(+), 25 deletions(-) diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c index bb514403e305..53e4c37441be 100644 --- a/drivers/block/zram/zcomp.c +++ b/drivers/block/zram/zcomp.c @@ -6,7 +6,7 @@ #include #include #include -#include +#include #include #include =20 @@ -109,13 +109,29 @@ ssize_t zcomp_available_show(const char *comp, char *= buf) =20 struct zcomp_strm *zcomp_stream_get(struct zcomp *comp) { - local_lock(&comp->stream->lock); - return this_cpu_ptr(comp->stream); + for (;;) { + struct zcomp_strm *zstrm =3D raw_cpu_ptr(comp->stream); + + /* + * Inspired by zswap + * + * stream is returned with ->mutex locked which prevents + * cpu_dead() from releasing this stream under us, however + * there is still a race window between raw_cpu_ptr() and + * mutex_lock(), during which we could have been migrated + * from a CPU that has already destroyed its stream. If + * so then unlock and re-try on the current CPU. + */ + mutex_lock(&zstrm->lock); + if (likely(zstrm->buffer)) + return zstrm; + mutex_unlock(&zstrm->lock); + } } =20 -void zcomp_stream_put(struct zcomp *comp) +void zcomp_stream_put(struct zcomp_strm *zstrm) { - local_unlock(&comp->stream->lock); + mutex_unlock(&zstrm->lock); } =20 int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm, @@ -151,12 +167,9 @@ int zcomp_decompress(struct zcomp *comp, struct zcomp_= strm *zstrm, int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node) { struct zcomp *comp =3D hlist_entry(node, struct zcomp, node); - struct zcomp_strm *zstrm; + struct zcomp_strm *zstrm =3D per_cpu_ptr(comp->stream, cpu); int ret; =20 - zstrm =3D per_cpu_ptr(comp->stream, cpu); - local_lock_init(&zstrm->lock); - ret =3D zcomp_strm_init(comp, zstrm); if (ret) pr_err("Can't allocate a compression stream\n"); @@ -166,16 +179,17 @@ int zcomp_cpu_up_prepare(unsigned int cpu, struct hli= st_node *node) int zcomp_cpu_dead(unsigned int cpu, struct hlist_node *node) { struct zcomp *comp =3D hlist_entry(node, struct zcomp, node); - struct zcomp_strm *zstrm; + struct zcomp_strm *zstrm =3D per_cpu_ptr(comp->stream, cpu); =20 - zstrm =3D per_cpu_ptr(comp->stream, cpu); + mutex_lock(&zstrm->lock); zcomp_strm_free(comp, zstrm); + mutex_unlock(&zstrm->lock); return 0; } =20 static int zcomp_init(struct zcomp *comp, struct zcomp_params *params) { - int ret; + int ret, cpu; =20 comp->stream =3D alloc_percpu(struct zcomp_strm); if (!comp->stream) @@ -186,6 +200,9 @@ static int zcomp_init(struct zcomp *comp, struct zcomp_= params *params) if (ret) goto cleanup; =20 + for_each_possible_cpu(cpu) + mutex_init(&per_cpu_ptr(comp->stream, cpu)->lock); + ret =3D cpuhp_state_add_instance(CPUHP_ZCOMP_PREPARE, &comp->node); if (ret < 0) goto cleanup; diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h index ad5762813842..23b8236b9090 100644 --- a/drivers/block/zram/zcomp.h +++ b/drivers/block/zram/zcomp.h @@ -3,7 +3,7 @@ #ifndef _ZCOMP_H_ #define _ZCOMP_H_ =20 -#include +#include =20 #define ZCOMP_PARAM_NO_LEVEL INT_MIN =20 @@ -31,7 +31,7 @@ struct zcomp_ctx { }; =20 struct zcomp_strm { - local_lock_t lock; + struct mutex lock; /* compression buffer */ void *buffer; struct zcomp_ctx ctx; @@ -77,7 +77,7 @@ struct zcomp *zcomp_create(const char *alg, struct zcomp_= params *params); void zcomp_destroy(struct zcomp *comp); =20 struct zcomp_strm *zcomp_stream_get(struct zcomp *comp); -void zcomp_stream_put(struct zcomp *comp); +void zcomp_stream_put(struct zcomp_strm *zstrm); =20 int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm, const void *src, unsigned int *dst_len); diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 37c5651305c2..1b5bb206239f 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1613,7 +1613,7 @@ static int read_compressed_page(struct zram *zram, st= ruct page *page, u32 index) ret =3D zcomp_decompress(zram->comps[prio], zstrm, src, size, dst); kunmap_local(dst); zs_unmap_object(zram->mem_pool, handle); - zcomp_stream_put(zram->comps[prio]); + zcomp_stream_put(zstrm); =20 return ret; } @@ -1774,14 +1774,14 @@ static int zram_write_page(struct zram *zram, struc= t page *page, u32 index) kunmap_local(mem); =20 if (unlikely(ret)) { - zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]); + zcomp_stream_put(zstrm); pr_err("Compression failed! err=3D%d\n", ret); zs_free(zram->mem_pool, handle); return ret; } =20 if (comp_len >=3D huge_class_size) { - zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]); + zcomp_stream_put(zstrm); return write_incompressible_page(zram, page, index); } =20 @@ -1805,7 +1805,7 @@ static int zram_write_page(struct zram *zram, struct = page *page, u32 index) __GFP_HIGHMEM | __GFP_MOVABLE); if (IS_ERR_VALUE(handle)) { - zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]); + zcomp_stream_put(zstrm); atomic64_inc(&zram->stats.writestall); handle =3D zs_malloc(zram->mem_pool, comp_len, GFP_NOIO | __GFP_HIGHMEM | @@ -1817,7 +1817,7 @@ static int zram_write_page(struct zram *zram, struct = page *page, u32 index) } =20 if (!zram_can_store_page(zram)) { - zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]); + zcomp_stream_put(zstrm); zs_free(zram->mem_pool, handle); return -ENOMEM; } @@ -1825,7 +1825,7 @@ static int zram_write_page(struct zram *zram, struct = page *page, u32 index) dst =3D zs_map_object(zram->mem_pool, handle, ZS_MM_WO); =20 memcpy(dst, zstrm->buffer, comp_len); - zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]); + zcomp_stream_put(zstrm); zs_unmap_object(zram->mem_pool, handle); =20 zram_slot_lock(zram, index); @@ -1984,7 +1984,7 @@ static int recompress_slot(struct zram *zram, u32 ind= ex, struct page *page, kunmap_local(src); =20 if (ret) { - zcomp_stream_put(zram->comps[prio]); + zcomp_stream_put(zstrm); return ret; } =20 @@ -1994,7 +1994,7 @@ static int recompress_slot(struct zram *zram, u32 ind= ex, struct page *page, /* Continue until we make progress */ if (class_index_new >=3D class_index_old || (threshold && comp_len_new >=3D threshold)) { - zcomp_stream_put(zram->comps[prio]); + zcomp_stream_put(zstrm); continue; } =20 @@ -2052,13 +2052,13 @@ static int recompress_slot(struct zram *zram, u32 i= ndex, struct page *page, __GFP_HIGHMEM | __GFP_MOVABLE); 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Fri, 21 Feb 2025 14:30:24 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v8 03/17] zram: remove unused crypto include Date: Sat, 22 Feb 2025 07:25:34 +0900 Message-ID: <20250221222958.2225035-4-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <20250221222958.2225035-1-senozhatsky@chromium.org> References: <20250221222958.2225035-1-senozhatsky@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" We stopped using crypto API (for the time being), so remove its include and replace CRYPTO_MAX_ALG_NAME with a local define. Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zcomp.c | 1 - drivers/block/zram/zram_drv.c | 4 +++- drivers/block/zram/zram_drv.h | 1 - 3 files changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c index 53e4c37441be..cfdde2e0748a 100644 --- a/drivers/block/zram/zcomp.c +++ b/drivers/block/zram/zcomp.c @@ -7,7 +7,6 @@ #include #include #include -#include #include =20 #include "zcomp.h" diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 1b5bb206239f..c73d8024f48f 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -44,6 +44,8 @@ static DEFINE_MUTEX(zram_index_mutex); static int zram_major; static const char *default_compressor =3D CONFIG_ZRAM_DEF_COMP; =20 +#define ZRAM_MAX_ALGO_NAME_SZ 128 + /* Module params (documentation at end) */ static unsigned int num_devices =3D 1; /* @@ -1154,7 +1156,7 @@ static int __comp_algorithm_store(struct zram *zram, = u32 prio, const char *buf) size_t sz; =20 sz =3D strlen(buf); - if (sz >=3D CRYPTO_MAX_ALG_NAME) + if (sz >=3D ZRAM_MAX_ALGO_NAME_SZ) return -E2BIG; =20 compressor =3D kstrdup(buf, GFP_KERNEL); diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h index 794c9234e627..2c380ea9a816 100644 --- a/drivers/block/zram/zram_drv.h +++ b/drivers/block/zram/zram_drv.h @@ -17,7 +17,6 @@ =20 #include #include -#include =20 #include "zcomp.h" =20 --=20 2.48.1.601.g30ceb7b040-goog From nobody Tue Dec 16 19:46:24 2025 Received: from mail-pl1-f170.google.com (mail-pl1-f170.google.com [209.85.214.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B388425332C for ; Fri, 21 Feb 2025 22:30:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.170 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740177032; cv=none; b=EurhFqYHw8D6sfs1OMoBUjtAxGbLorEc6n2h60eKzeRJFJG89E9I3S2qFoZbQD8m3bgXaKtzmBMCYgLyM3JMX2+VbfsD22H9806QxIcjrHvlOm4jROVUdv+sqjHWv8eQwv74ZCO0SxZO7KeEnQ+scVz2rtdNy8HTrxGEODu4y8c= ARC-Message-Signature: i=1; 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Fri, 21 Feb 2025 14:30:29 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v8 04/17] zram: remove max_comp_streams device attr Date: Sat, 22 Feb 2025 07:25:35 +0900 Message-ID: <20250221222958.2225035-5-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <20250221222958.2225035-1-senozhatsky@chromium.org> References: <20250221222958.2225035-1-senozhatsky@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" max_comp_streams device attribute has been defunct since May 2016 when zram switched to per-CPU compression streams, remove it. Signed-off-by: Sergey Senozhatsky --- Documentation/ABI/testing/sysfs-block-zram | 8 ----- Documentation/admin-guide/blockdev/zram.rst | 36 ++++++--------------- drivers/block/zram/zram_drv.c | 23 ------------- 3 files changed, 10 insertions(+), 57 deletions(-) diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI= /testing/sysfs-block-zram index 1ef69e0271f9..36c57de0a10a 100644 --- a/Documentation/ABI/testing/sysfs-block-zram +++ b/Documentation/ABI/testing/sysfs-block-zram @@ -22,14 +22,6 @@ Description: device. The reset operation frees all the memory associated with this device. =20 -What: /sys/block/zram/max_comp_streams -Date: February 2014 -Contact: Sergey Senozhatsky -Description: - The max_comp_streams file is read-write and specifies the - number of backend's zcomp_strm compression streams (number of - concurrent compress operations). - What: /sys/block/zram/comp_algorithm Date: February 2014 Contact: Sergey Senozhatsky diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/ad= min-guide/blockdev/zram.rst index 714a5171bfc0..7ad4c86f8258 100644 --- a/Documentation/admin-guide/blockdev/zram.rst +++ b/Documentation/admin-guide/blockdev/zram.rst @@ -54,7 +54,7 @@ The list of possible return codes: If you use 'echo', the returned value is set by the 'echo' utility, and, in general case, something like:: =20 - echo 3 > /sys/block/zram0/max_comp_streams + echo foo > /sys/block/zram0/comp_algorithm if [ $? -ne 0 ]; then handle_error fi @@ -73,21 +73,7 @@ This creates 4 devices: /dev/zram{0,1,2,3} num_devices parameter is optional and tells zram how many devices should be pre-created. Default: 1. =20 -2) Set max number of compression streams -=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D - -Regardless of the value passed to this attribute, ZRAM will always -allocate multiple compression streams - one per online CPU - thus -allowing several concurrent compression operations. The number of -allocated compression streams goes down when some of the CPUs -become offline. There is no single-compression-stream mode anymore, -unless you are running a UP system or have only 1 CPU online. - -To find out how many streams are currently available:: - - cat /sys/block/zram0/max_comp_streams - -3) Select compression algorithm +2) Select compression algorithm =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D =20 Using comp_algorithm device attribute one can see available and @@ -107,7 +93,7 @@ Examples:: For the time being, the `comp_algorithm` content shows only compression algorithms that are supported by zram. =20 -4) Set compression algorithm parameters: Optional +3) Set compression algorithm parameters: Optional =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20 Compression algorithms may support specific parameters which can be @@ -138,7 +124,7 @@ better the compression ratio, it even can take negative= s values for some algorithms), for other algorithms `level` is acceleration level (the higher the value the lower the compression ratio). =20 -5) Set Disksize +4) Set Disksize =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20 Set disk size by writing the value to sysfs node 'disksize'. @@ -158,7 +144,7 @@ There is little point creating a zram of greater than t= wice the size of memory since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of= the size of the disk when not in use so a huge zram is wasteful. =20 -6) Set memory limit: Optional +5) Set memory limit: Optional =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D =20 Set memory limit by writing the value to sysfs node 'mem_limit'. @@ -177,7 +163,7 @@ Examples:: # To disable memory limit echo 0 > /sys/block/zram0/mem_limit =20 -7) Activate +6) Activate =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20 :: @@ -188,7 +174,7 @@ Examples:: mkfs.ext4 /dev/zram1 mount /dev/zram1 /tmp =20 -8) Add/remove zram devices +7) Add/remove zram devices =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D =20 zram provides a control interface, which enables dynamic (on-demand) device @@ -208,7 +194,7 @@ execute:: =20 echo X > /sys/class/zram-control/hot_remove =20 -9) Stats +8) Stats =3D=3D=3D=3D=3D=3D=3D=3D =20 Per-device statistics are exported as various nodes under /sys/block/zram<= id>/ @@ -228,8 +214,6 @@ mem_limit WO specifies the maximum amount of m= emory ZRAM can writeback_limit WO specifies the maximum amount of write IO zram can write out to backing device as 4KB unit writeback_limit_enable RW show and set writeback_limit feature -max_comp_streams RW the number of possible concurrent compress - operations comp_algorithm RW show and change the compression algorithm algorithm_params WO setup compression algorithm parameters compact WO trigger memory compaction @@ -310,7 +294,7 @@ a single line of text and contains the following stats = separated by whitespace: Unit: 4K bytes =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D =20 -10) Deactivate +9) Deactivate =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20 :: @@ -318,7 +302,7 @@ a single line of text and contains the following stats = separated by whitespace: swapoff /dev/zram0 umount /dev/zram1 =20 -11) Reset +10) Reset =3D=3D=3D=3D=3D=3D=3D=3D=3D =20 Write any positive value to 'reset' sysfs node:: diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index c73d8024f48f..c7bc0c9f3f2f 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1109,27 +1109,6 @@ static void zram_debugfs_register(struct zram *zram)= {}; static void zram_debugfs_unregister(struct zram *zram) {}; #endif =20 -/* - * We switched to per-cpu streams and this attr is not needed anymore. - * However, we will keep it around for some time, because: - * a) we may revert per-cpu streams in the future - * b) it's visible to user space and we need to follow our 2 years - * retirement rule; but we already have a number of 'soon to be - * altered' attrs, so max_comp_streams need to wait for the next - * layoff cycle. - */ -static ssize_t max_comp_streams_show(struct device *dev, - struct device_attribute *attr, char *buf) -{ - return scnprintf(buf, PAGE_SIZE, "%d\n", num_online_cpus()); -} - -static ssize_t max_comp_streams_store(struct device *dev, - struct device_attribute *attr, const char *buf, size_t len) -{ - return len; -} - static void comp_algorithm_set(struct zram *zram, u32 prio, const char *al= g) { /* Do not free statically defined compression algorithms */ @@ -2546,7 +2525,6 @@ static DEVICE_ATTR_WO(reset); static DEVICE_ATTR_WO(mem_limit); 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charset="utf-8" Previously zram write() was atomic which required us to pass __GFP_KSWAPD_RECLAIM to zsmalloc handle allocation on a fast path and attempt a slow path allocation (with recompression) if the fast path failed. Since we are not in atomic context anymore we can permit direct reclaim during handle allocation, and hence can have a single allocation path. There is no slow path anymore so we don't unlock per-CPU stream (and don't lose compressed data) which means that there is no need to do recompression now (which should reduce CPU and battery usage). Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zram_drv.c | 38 ++++++----------------------------- 1 file changed, 6 insertions(+), 32 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index c7bc0c9f3f2f..4ccc1a1a8f20 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1729,11 +1729,11 @@ static int write_incompressible_page(struct zram *z= ram, struct page *page, static int zram_write_page(struct zram *zram, struct page *page, u32 index) { int ret =3D 0; - unsigned long handle =3D -ENOMEM; - unsigned int comp_len =3D 0; + unsigned long handle; + unsigned int comp_len; void *dst, *mem; struct zcomp_strm *zstrm; - unsigned long element =3D 0; + unsigned long element; bool same_filled; =20 /* First, free memory allocated to this slot (if any) */ @@ -1747,7 +1747,6 @@ static int zram_write_page(struct zram *zram, struct = page *page, u32 index) if (same_filled) return write_same_filled_page(zram, element, index); =20 -compress_again: zstrm =3D zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]); mem =3D kmap_local_page(page); ret =3D zcomp_compress(zram->comps[ZRAM_PRIMARY_COMP], zstrm, @@ -1757,7 +1756,6 @@ static int zram_write_page(struct zram *zram, struct = page *page, u32 index) if (unlikely(ret)) { zcomp_stream_put(zstrm); pr_err("Compression failed! err=3D%d\n", ret); - zs_free(zram->mem_pool, handle); return ret; } =20 @@ -1766,35 +1764,11 @@ static int zram_write_page(struct zram *zram, struc= t page *page, u32 index) return write_incompressible_page(zram, page, index); } =20 - /* - * handle allocation has 2 paths: - * a) fast path is executed with preemption disabled (for - * per-cpu streams) and has __GFP_DIRECT_RECLAIM bit clear, - * since we can't sleep; - * b) slow path enables preemption and attempts to allocate - * the page with __GFP_DIRECT_RECLAIM bit set. we have to - * put per-cpu compression stream and, thus, to re-do - * the compression once handle is allocated. - * - * if we have a 'non-null' handle here then we are coming - * from the slow path and handle has already been allocated. - */ - if (IS_ERR_VALUE(handle)) - handle =3D zs_malloc(zram->mem_pool, comp_len, - __GFP_KSWAPD_RECLAIM | - __GFP_NOWARN | - __GFP_HIGHMEM | - __GFP_MOVABLE); 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Fri, 21 Feb 2025 14:30:39 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v8 06/17] zram: remove writestall zram_stats member Date: Sat, 22 Feb 2025 07:25:37 +0900 Message-ID: <20250221222958.2225035-7-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <20250221222958.2225035-1-senozhatsky@chromium.org> References: <20250221222958.2225035-1-senozhatsky@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" There is no zsmalloc handle allocation slow path now and writestall is not possible any longer. Remove it from zram_stats. Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zram_drv.c | 3 +-- drivers/block/zram/zram_drv.h | 1 - 2 files changed, 1 insertion(+), 3 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 4ccc1a1a8f20..710b10c6e336 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1443,9 +1443,8 @@ static ssize_t debug_stat_show(struct device *dev, =20 down_read(&zram->init_lock); ret =3D scnprintf(buf, PAGE_SIZE, - "version: %d\n%8llu %8llu\n", + "version: %d\n0 %8llu\n", version, - (u64)atomic64_read(&zram->stats.writestall), (u64)atomic64_read(&zram->stats.miss_free)); up_read(&zram->init_lock); =20 diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h index 2c380ea9a816..59c75154524f 100644 --- a/drivers/block/zram/zram_drv.h +++ b/drivers/block/zram/zram_drv.h @@ -84,7 +84,6 @@ struct zram_stats { atomic64_t huge_pages_since; /* no. of huge pages since zram set up */ atomic64_t pages_stored; 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Fri, 21 Feb 2025 14:30:45 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v8 07/17] zram: limit max recompress prio to num_active_comps Date: Sat, 22 Feb 2025 07:25:38 +0900 Message-ID: <20250221222958.2225035-8-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <20250221222958.2225035-1-senozhatsky@chromium.org> References: <20250221222958.2225035-1-senozhatsky@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Use the actual number of algorithms zram was configure with instead of theoretical limit of ZRAM_MAX_COMPS. Also make sure that min prio is not above max prio. Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zram_drv.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 710b10c6e336..b32b959046af 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -2031,16 +2031,19 @@ static ssize_t recompress_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t len) { - u32 prio =3D ZRAM_SECONDARY_COMP, prio_max =3D ZRAM_MAX_COMPS; struct zram *zram =3D dev_to_zram(dev); char *args, *param, *val, *algo =3D NULL; u64 num_recomp_pages =3D ULLONG_MAX; struct zram_pp_ctl *ctl =3D NULL; struct zram_pp_slot *pps; u32 mode =3D 0, threshold =3D 0; + u32 prio, prio_max; struct page *page; ssize_t ret; =20 + prio =3D ZRAM_SECONDARY_COMP; + prio_max =3D zram->num_active_comps; + args =3D skip_spaces(buf); while (*args) { args =3D next_arg(args, ¶m, &val); @@ -2093,7 +2096,7 @@ static ssize_t recompress_store(struct device *dev, if (prio =3D=3D ZRAM_PRIMARY_COMP) prio =3D ZRAM_SECONDARY_COMP; 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charset="utf-8" Do no select for post processing slots that are already compressed with same or higher priority compression algorithm. This should save some memory, as previously we would still put those entries into corresponding post-processing buckets and filter them out later in recompress_slot(). Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zram_drv.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index b32b959046af..92908495c904 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1827,7 +1827,7 @@ static int zram_bvec_write(struct zram *zram, struct = bio_vec *bvec, #define RECOMPRESS_IDLE (1 << 0) #define RECOMPRESS_HUGE (1 << 1) =20 -static int scan_slots_for_recompress(struct zram *zram, u32 mode, +static int scan_slots_for_recompress(struct zram *zram, u32 mode, u32 prio= _max, struct zram_pp_ctl *ctl) { unsigned long nr_pages =3D zram->disksize >> PAGE_SHIFT; @@ -1859,6 +1859,10 @@ static int scan_slots_for_recompress(struct zram *zr= am, u32 mode, zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE)) goto next; =20 + /* Already compressed with same of higher priority */ + if (zram_get_priority(zram, index) + 1 >=3D prio_max) + goto next; + pps->index =3D index; place_pp_slot(zram, ctl, pps); pps =3D NULL; @@ -1915,6 +1919,16 @@ static int recompress_slot(struct zram *zram, u32 in= dex, struct page *page, zram_clear_flag(zram, index, ZRAM_IDLE); =20 class_index_old =3D zs_lookup_class_index(zram->mem_pool, comp_len_old); + + prio =3D max(prio, zram_get_priority(zram, index) + 1); + /* + * Recompression slots scan should not select slots that are + * already compressed with a higher priority algorithm, but + * just in case + */ + if (prio >=3D prio_max) + return 0; + /* * Iterate the secondary comp algorithms list (in order of priority) * and try to recompress the page. @@ -1923,13 +1937,6 @@ static int recompress_slot(struct zram *zram, u32 in= dex, struct page *page, if (!zram->comps[prio]) continue; =20 - /* - * Skip if the object is already re-compressed with a higher - * priority algorithm (or same algorithm). - */ - if (prio <=3D zram_get_priority(zram, index)) - continue; - num_recomps++; zstrm =3D zcomp_stream_get(zram->comps[prio]); 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Fri, 21 Feb 2025 14:30:56 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v8 09/17] zram: rework recompression loop Date: Sat, 22 Feb 2025 07:25:40 +0900 Message-ID: <20250221222958.2225035-10-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <20250221222958.2225035-1-senozhatsky@chromium.org> References: <20250221222958.2225035-1-senozhatsky@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" This reworks recompression loop handling: - set a rule that stream-put NULLs the stream pointer If the loop returns with a non-NULL stream then it's a successfull recompression, otherwise the stream should always be NULL. - do not count the number of recompressions Mark object as incompressible as soon as the algorithm with the highest priority failed to compress that object. - count compression errors as resource usage Even if compression has failed, we still need to bump num_recomp_pages counter. Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zram_drv.c | 53 +++++++++++++---------------------- 1 file changed, 19 insertions(+), 34 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 92908495c904..b96be8576cbc 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1892,9 +1892,8 @@ static int recompress_slot(struct zram *zram, u32 ind= ex, struct page *page, unsigned int comp_len_new; unsigned int class_index_old; unsigned int class_index_new; - u32 num_recomps =3D 0; void *src, *dst; - int ret; + int ret =3D 0; =20 handle_old =3D zram_get_handle(zram, index); if (!handle_old) @@ -1937,7 +1936,6 @@ static int recompress_slot(struct zram *zram, u32 ind= ex, struct page *page, if (!zram->comps[prio]) continue; =20 - num_recomps++; zstrm =3D zcomp_stream_get(zram->comps[prio]); src =3D kmap_local_page(page); ret =3D zcomp_compress(zram->comps[prio], zstrm, @@ -1946,7 +1944,8 @@ static int recompress_slot(struct zram *zram, u32 ind= ex, struct page *page, =20 if (ret) { zcomp_stream_put(zstrm); - return ret; + zstrm =3D NULL; + break; } =20 class_index_new =3D zs_lookup_class_index(zram->mem_pool, @@ -1956,6 +1955,7 @@ static int recompress_slot(struct zram *zram, u32 ind= ex, struct page *page, if (class_index_new >=3D class_index_old || (threshold && comp_len_new >=3D threshold)) { zcomp_stream_put(zstrm); + zstrm =3D NULL; continue; } =20 @@ -1963,14 +1963,6 @@ static int recompress_slot(struct zram *zram, u32 in= dex, struct page *page, break; } =20 - /* - * We did not try to recompress, e.g. when we have only one - * secondary algorithm and the page is already recompressed - * using that algorithm - */ - if (!zstrm) - return 0; - /* * Decrement the limit (if set) on pages we can recompress, even * when current recompression was unsuccessful or did not compress @@ -1980,38 +1972,31 @@ static int recompress_slot(struct zram *zram, u32 i= ndex, struct page *page, if (*num_recomp_pages) *num_recomp_pages -=3D 1; =20 - if (class_index_new >=3D class_index_old) { + /* Compression error */ + if (ret) + return ret; + + if (!zstrm) { /* * Secondary algorithms failed to re-compress the page - * in a way that would save memory, mark the object as - * incompressible so that we will not try to compress - * it again. + * in a way that would save memory. * - * We need to make sure that all secondary algorithms have - * failed, so we test if the number of recompressions matches - * the number of active secondary algorithms. + * Mark the object incompressible if the max-priority + * algorithm couldn't re-compress it. */ - if (num_recomps =3D=3D zram->num_active_comps - 1) - zram_set_flag(zram, index, ZRAM_INCOMPRESSIBLE); + if (prio < zram->num_active_comps) + return 0; + zram_set_flag(zram, index, ZRAM_INCOMPRESSIBLE); return 0; } =20 - /* Successful recompression but above threshold */ - if (threshold && comp_len_new >=3D threshold) - return 0; - /* - * No direct reclaim (slow path) for handle allocation and no - * re-compression attempt (unlike in zram_write_bvec()) since - * we already have stored that object in zsmalloc. 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Fri, 21 Feb 2025 14:31:02 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v8 10/17] zsmalloc: rename pool lock Date: Sat, 22 Feb 2025 07:25:41 +0900 Message-ID: <20250221222958.2225035-11-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <20250221222958.2225035-1-senozhatsky@chromium.org> References: <20250221222958.2225035-1-senozhatsky@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The old name comes from the times when the pool did not have compaction (defragmentation). Rename it to ->lock because these days it synchronizes not only migration. Reviewed-by: Yosry Ahmed Signed-off-by: Sergey Senozhatsky --- mm/zsmalloc.c | 38 +++++++++++++++++++------------------- 1 file changed, 19 insertions(+), 19 deletions(-) diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 817626a351f8..1424ee73cbb5 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -18,7 +18,7 @@ /* * lock ordering: * page_lock - * pool->migrate_lock + * pool->lock * class->lock * zspage->lock */ @@ -223,8 +223,8 @@ struct zs_pool { #ifdef CONFIG_COMPACTION struct work_struct free_work; #endif - /* protect page/zspage migration */ - rwlock_t migrate_lock; + /* protect zspage migration/compaction */ + rwlock_t lock; atomic_t compaction_in_progress; }; =20 @@ -1206,7 +1206,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned lo= ng handle, BUG_ON(in_interrupt()); =20 /* It guarantees it can get zspage from handle safely */ - read_lock(&pool->migrate_lock); + read_lock(&pool->lock); obj =3D handle_to_obj(handle); obj_to_location(obj, &zpdesc, &obj_idx); zspage =3D get_zspage(zpdesc); @@ -1218,7 +1218,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned lo= ng handle, * which is smaller granularity. */ migrate_read_lock(zspage); - read_unlock(&pool->migrate_lock); + read_unlock(&pool->lock); =20 class =3D zspage_class(pool, zspage); off =3D offset_in_page(class->size * obj_idx); @@ -1450,16 +1450,16 @@ void zs_free(struct zs_pool *pool, unsigned long ha= ndle) return; =20 /* - * The pool->migrate_lock protects the race with zpage's migration + * The pool->lock protects the race with zpage's migration * so it's safe to get the page from handle. */ - read_lock(&pool->migrate_lock); + read_lock(&pool->lock); obj =3D handle_to_obj(handle); obj_to_zpdesc(obj, &f_zpdesc); zspage =3D get_zspage(f_zpdesc); class =3D zspage_class(pool, zspage); spin_lock(&class->lock); - read_unlock(&pool->migrate_lock); + read_unlock(&pool->lock); =20 class_stat_sub(class, ZS_OBJS_INUSE, 1); obj_free(class->size, obj); @@ -1796,7 +1796,7 @@ static int zs_page_migrate(struct page *newpage, stru= ct page *page, * The pool migrate_lock protects the race between zpage migration * and zs_free. */ - write_lock(&pool->migrate_lock); + write_lock(&pool->lock); class =3D zspage_class(pool, zspage); =20 /* @@ -1833,7 +1833,7 @@ static int zs_page_migrate(struct page *newpage, stru= ct page *page, * Since we complete the data copy and set up new zspage structure, * it's okay to release migration_lock. */ - write_unlock(&pool->migrate_lock); + write_unlock(&pool->lock); spin_unlock(&class->lock); migrate_write_unlock(zspage); =20 @@ -1956,7 +1956,7 @@ static unsigned long __zs_compact(struct zs_pool *poo= l, * protect the race between zpage migration and zs_free * as well as zpage allocation/free */ - write_lock(&pool->migrate_lock); + write_lock(&pool->lock); spin_lock(&class->lock); while (zs_can_compact(class)) { int fg; @@ -1983,14 +1983,14 @@ static unsigned long __zs_compact(struct zs_pool *p= ool, src_zspage =3D NULL; =20 if (get_fullness_group(class, dst_zspage) =3D=3D ZS_INUSE_RATIO_100 - || rwlock_is_contended(&pool->migrate_lock)) { + || rwlock_is_contended(&pool->lock)) { putback_zspage(class, dst_zspage); dst_zspage =3D NULL; =20 spin_unlock(&class->lock); - write_unlock(&pool->migrate_lock); + write_unlock(&pool->lock); cond_resched(); - write_lock(&pool->migrate_lock); + write_lock(&pool->lock); spin_lock(&class->lock); } } @@ -2002,7 +2002,7 @@ static unsigned long __zs_compact(struct zs_pool *poo= l, putback_zspage(class, dst_zspage); =20 spin_unlock(&class->lock); - write_unlock(&pool->migrate_lock); + write_unlock(&pool->lock); =20 return pages_freed; } @@ -2014,10 +2014,10 @@ unsigned long zs_compact(struct zs_pool *pool) unsigned long pages_freed =3D 0; =20 /* - * Pool compaction is performed under pool->migrate_lock so it is basical= ly + * Pool compaction is performed under pool->lock so it is basically * single-threaded. 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Fri, 21 Feb 2025 14:31:09 -0800 (PST) Received: from localhost ([2401:fa00:8f:203:f987:e1e:3dbb:2191]) by smtp.gmail.com with UTF8SMTPSA id d9443c01a7336-220d545df28sm141974715ad.153.2025.02.21.14.31.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Feb 2025 14:31:09 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v8 11/17] zsmalloc: make zspage lock preemptible Date: Sat, 22 Feb 2025 07:25:42 +0900 Message-ID: <20250221222958.2225035-12-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <20250221222958.2225035-1-senozhatsky@chromium.org> References: <20250221222958.2225035-1-senozhatsky@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" In order to implement preemptible object mapping we need a zspage lock that satisfies several preconditions: - it should be reader-write type of a lock - it should be possible to hold it from any context, but also being preemptible if the context allows it - we never sleep while acquiring but can sleep while holding in read mode An rwsemaphore doesn't suffice, due to atomicity requirements, rwlock doesn't satisfy due to reader-preemptability requirement. It's also worth to mention, that per-zspage rwsem is a little too memory heavy (we can easily have double digits megabytes used only on rwsemaphores). Switch over from rwlock_t to a atomic_t-based implementation of a reader-writer semaphore that satisfies all of the preconditions. The spin-lock based zspage_lock is suggested by Hillf Danton. Suggested-by: Hillf Danton Signed-off-by: Sergey Senozhatsky --- mm/zsmalloc.c | 184 +++++++++++++++++++++++++++++++++++--------------- 1 file changed, 131 insertions(+), 53 deletions(-) diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 1424ee73cbb5..03710d71d022 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -226,6 +226,9 @@ struct zs_pool { /* protect zspage migration/compaction */ rwlock_t lock; atomic_t compaction_in_progress; +#ifdef CONFIG_DEBUG_LOCK_ALLOC + struct lock_class_key lock_class; +#endif }; =20 static inline void zpdesc_set_first(struct zpdesc *zpdesc) @@ -257,6 +260,18 @@ static inline void free_zpdesc(struct zpdesc *zpdesc) __free_page(page); } =20 +#define ZS_PAGE_UNLOCKED 0 +#define ZS_PAGE_WRLOCKED -1 + +struct zspage_lock { + spinlock_t lock; + int cnt; + +#ifdef CONFIG_DEBUG_LOCK_ALLOC + struct lockdep_map dep_map; +#endif +}; + struct zspage { struct { unsigned int huge:HUGE_BITS; @@ -269,7 +284,7 @@ struct zspage { struct zpdesc *first_zpdesc; struct list_head list; /* fullness list */ struct zs_pool *pool; - rwlock_t lock; + struct zspage_lock zsl; }; =20 struct mapping_area { @@ -279,6 +294,93 @@ struct mapping_area { enum zs_mapmode vm_mm; /* mapping mode */ }; =20 +#ifdef CONFIG_DEBUG_LOCK_ALLOC +#define zsl_dep_map(zsl) (&(zsl)->dep_map) +#define zspool_lock_class(pool) (&(pool)->lock_class) +#else +#define zsl_dep_map(zsl) NULL +#define zspool_lock_class(pool) NULL +#endif + +static void zspage_lock_init(struct zspage *zspage) +{ + struct zspage_lock *zsl =3D &zspage->zsl; + + lockdep_init_map(zsl_dep_map(zsl), "zspage->lock", + zspool_lock_class(zspage->pool), 0); + spin_lock_init(&zsl->lock); + zsl->cnt =3D ZS_PAGE_UNLOCKED; +} + +/* + * The zspage lock can be held from atomic contexts, but it needs to remain + * preemptible when held for reading because it remains held outside of th= ose + * atomic contexts, otherwise we unnecessarily lose preemptibility. + * + * To achieve this, the following rules are enforced on readers and writer= s: + * + * - Writers are blocked by both writers and readers, while readers are on= ly + * blocked by writers (i.e. normal rwlock semantics). + * + * - Writers are always atomic (to allow readers to spin waiting for them). + * + * - Writers always use trylock (as the lock may be held be sleeping reade= rs). + * + * - Readers may spin on the lock (as they can only wait for atomic writer= s). + * + * - Readers may sleep while holding the lock (as writes only use trylock). + */ +static void zspage_read_lock(struct zspage *zspage) +{ + struct zspage_lock *zsl =3D &zspage->zsl; + + rwsem_acquire_read(zsl_dep_map(zsl), 0, 0, _RET_IP_); + + spin_lock(&zsl->lock); + zsl->cnt++; + spin_unlock(&zsl->lock); + + lock_acquired(zsl_dep_map(zsl), _RET_IP_); +} + +static void zspage_read_unlock(struct zspage *zspage) +{ + struct zspage_lock *zsl =3D &zspage->zsl; + + rwsem_release(zsl_dep_map(zsl), _RET_IP_); + + spin_lock(&zsl->lock); + zsl->cnt--; + spin_unlock(&zsl->lock); +} + +static __must_check bool zspage_write_trylock(struct zspage *zspage) +{ + struct zspage_lock *zsl =3D &zspage->zsl; + + spin_lock(&zsl->lock); + if (zsl->cnt =3D=3D ZS_PAGE_UNLOCKED) { + zsl->cnt =3D ZS_PAGE_WRLOCKED; + rwsem_acquire(zsl_dep_map(zsl), 0, 1, _RET_IP_); + lock_acquired(zsl_dep_map(zsl), _RET_IP_); + return true; + } + + lock_contended(zsl_dep_map(zsl), _RET_IP_); + spin_unlock(&zsl->lock); + return false; +} + +static void zspage_write_unlock(struct zspage *zspage) +{ + struct zspage_lock *zsl =3D &zspage->zsl; + + rwsem_release(zsl_dep_map(zsl), _RET_IP_); + + zsl->cnt =3D ZS_PAGE_UNLOCKED; + spin_unlock(&zsl->lock); +} + /* huge object: pages_per_zspage =3D=3D 1 && maxobj_per_zspage =3D=3D 1 */ static void SetZsHugePage(struct zspage *zspage) { @@ -290,12 +392,6 @@ static bool ZsHugePage(struct zspage *zspage) return zspage->huge; } =20 -static void migrate_lock_init(struct zspage *zspage); -static void migrate_read_lock(struct zspage *zspage); -static void migrate_read_unlock(struct zspage *zspage); -static void migrate_write_lock(struct zspage *zspage); -static void migrate_write_unlock(struct zspage *zspage); - #ifdef CONFIG_COMPACTION static void kick_deferred_free(struct zs_pool *pool); static void init_deferred_free(struct zs_pool *pool); @@ -992,7 +1088,9 @@ static struct zspage *alloc_zspage(struct zs_pool *poo= l, return NULL; =20 zspage->magic =3D ZSPAGE_MAGIC; - migrate_lock_init(zspage); + zspage->pool =3D pool; + zspage->class =3D class->index; + zspage_lock_init(zspage); =20 for (i =3D 0; i < class->pages_per_zspage; i++) { struct zpdesc *zpdesc; @@ -1015,8 +1113,6 @@ static struct zspage *alloc_zspage(struct zs_pool *po= ol, =20 create_page_chain(class, zspage, zpdescs); init_zspage(class, zspage); - zspage->pool =3D pool; - zspage->class =3D class->index; =20 return zspage; } @@ -1217,7 +1313,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned lo= ng handle, * zs_unmap_object API so delegate the locking from class to zspage * which is smaller granularity. */ - migrate_read_lock(zspage); + zspage_read_lock(zspage); read_unlock(&pool->lock); =20 class =3D zspage_class(pool, zspage); @@ -1277,7 +1373,7 @@ void zs_unmap_object(struct zs_pool *pool, unsigned l= ong handle) } local_unlock(&zs_map_area.lock); =20 - migrate_read_unlock(zspage); + zspage_read_unlock(zspage); } EXPORT_SYMBOL_GPL(zs_unmap_object); =20 @@ -1671,18 +1767,18 @@ static void lock_zspage(struct zspage *zspage) /* * Pages we haven't locked yet can be migrated off the list while we're * trying to lock them, so we need to be careful and only attempt to - * lock each page under migrate_read_lock(). Otherwise, the page we lock + * lock each page under zspage_read_lock(). Otherwise, the page we lock * may no longer belong to the zspage. This means that we may wait for * the wrong page to unlock, so we must take a reference to the page - * prior to waiting for it to unlock outside migrate_read_lock(). + * prior to waiting for it to unlock outside zspage_read_lock(). */ while (1) { - migrate_read_lock(zspage); + zspage_read_lock(zspage); zpdesc =3D get_first_zpdesc(zspage); if (zpdesc_trylock(zpdesc)) break; zpdesc_get(zpdesc); - migrate_read_unlock(zspage); + zspage_read_unlock(zspage); zpdesc_wait_locked(zpdesc); zpdesc_put(zpdesc); } @@ -1693,41 +1789,16 @@ static void lock_zspage(struct zspage *zspage) curr_zpdesc =3D zpdesc; } else { zpdesc_get(zpdesc); - migrate_read_unlock(zspage); + zspage_read_unlock(zspage); zpdesc_wait_locked(zpdesc); zpdesc_put(zpdesc); - migrate_read_lock(zspage); + zspage_read_lock(zspage); } } - migrate_read_unlock(zspage); + zspage_read_unlock(zspage); } #endif /* CONFIG_COMPACTION */ =20 -static void migrate_lock_init(struct zspage *zspage) -{ - rwlock_init(&zspage->lock); -} - -static void migrate_read_lock(struct zspage *zspage) __acquires(&zspage->l= ock) -{ - read_lock(&zspage->lock); -} - -static void migrate_read_unlock(struct zspage *zspage) __releases(&zspage-= >lock) -{ - read_unlock(&zspage->lock); -} - -static void migrate_write_lock(struct zspage *zspage) -{ - write_lock(&zspage->lock); -} - -static void migrate_write_unlock(struct zspage *zspage) -{ - write_unlock(&zspage->lock); -} - #ifdef CONFIG_COMPACTION =20 static const struct movable_operations zsmalloc_mops; @@ -1785,9 +1856,6 @@ static int zs_page_migrate(struct page *newpage, stru= ct page *page, =20 VM_BUG_ON_PAGE(!zpdesc_is_isolated(zpdesc), zpdesc_page(zpdesc)); =20 - /* We're committed, tell the world that this is a Zsmalloc page. */ - __zpdesc_set_zsmalloc(newzpdesc); - /* The page is locked, so this pointer must remain valid */ zspage =3D get_zspage(zpdesc); pool =3D zspage->pool; @@ -1803,8 +1871,15 @@ static int zs_page_migrate(struct page *newpage, str= uct page *page, * the class lock protects zpage alloc/free in the zspage. */ spin_lock(&class->lock); - /* the migrate_write_lock protects zpage access via zs_map_object */ - migrate_write_lock(zspage); + /* the zspage write_lock protects zpage access via zs_map_object */ + if (!zspage_write_trylock(zspage)) { + spin_unlock(&class->lock); + write_unlock(&pool->lock); + return -EINVAL; + } + + /* We're committed, tell the world that this is a Zsmalloc page. */ + __zpdesc_set_zsmalloc(newzpdesc); =20 offset =3D get_first_obj_offset(zpdesc); s_addr =3D kmap_local_zpdesc(zpdesc); @@ -1835,7 +1910,7 @@ static int zs_page_migrate(struct page *newpage, stru= ct page *page, */ write_unlock(&pool->lock); spin_unlock(&class->lock); - migrate_write_unlock(zspage); + zspage_write_unlock(zspage); =20 zpdesc_get(newzpdesc); if (zpdesc_zone(newzpdesc) !=3D zpdesc_zone(zpdesc)) { @@ -1971,9 +2046,11 @@ static unsigned long __zs_compact(struct zs_pool *po= ol, if (!src_zspage) break; =20 - migrate_write_lock(src_zspage); + if (!zspage_write_trylock(src_zspage)) + break; + migrate_zspage(pool, src_zspage, dst_zspage); - migrate_write_unlock(src_zspage); + zspage_write_unlock(src_zspage); =20 fg =3D putback_zspage(class, src_zspage); if (fg =3D=3D ZS_INUSE_RATIO_0) { @@ -2141,6 +2218,7 @@ struct zs_pool *zs_create_pool(const char *name) init_deferred_free(pool); rwlock_init(&pool->lock); atomic_set(&pool->compaction_in_progress, 0); + lockdep_register_key(zspool_lock_class(pool)); =20 pool->name =3D kstrdup(name, GFP_KERNEL); if (!pool->name) @@ -2233,7 +2311,6 @@ struct zs_pool *zs_create_pool(const char *name) * trigger compaction manually. 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Fri, 21 Feb 2025 14:31:14 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v8 12/17] zsmalloc: introduce new object mapping API Date: Sat, 22 Feb 2025 07:25:43 +0900 Message-ID: <20250221222958.2225035-13-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <20250221222958.2225035-1-senozhatsky@chromium.org> References: <20250221222958.2225035-1-senozhatsky@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Current object mapping API is a little cumbersome. First, it's inconsistent, sometimes it returns with page-faults disabled and sometimes with page-faults enabled. Second, and most importantly, it enforces atomicity restrictions on its users. zs_map_object() has to return a liner object address which is not always possible because some objects span multiple physical (non-contiguous) pages. For such objects zsmalloc uses a per-CPU buffer to which object's data is copied before a pointer to that per-CPU buffer is returned back to the caller. This leads to another, final, issue - extra memcpy(). Since the caller gets a pointer to per-CPU buffer it can memcpy() data only to that buffer, and during zs_unmap_object() zsmalloc will memcpy() from that per-CPU buffer to physical pages that object in question spans across. New API splits functions by access mode: - zs_obj_read_begin(handle, local_copy) Returns a pointer to handle memory. For objects that span two physical pages a local_copy buffer is used to store object's data before the address is returned to the caller. Otherwise the object's page is kmap_local mapped directly. - zs_obj_read_end(handle, buf) Unmaps the page if it was kmap_local mapped by zs_obj_read_begin(). - zs_obj_write(handle, buf, len) Copies len-bytes from compression buffer to handle memory (takes care of objects that span two pages). This does not need any additional (e.g. per-CPU) buffers and writes the data directly to zsmalloc pool pages. In terms of performance, on a synthetic and completely reproducible test that allocates fixed number of objects of fixed sizes and iterates over those objects, first mapping in RO then in RW mode: OLD API =3D=3D=3D=3D=3D=3D=3D 3 first results out of 10 369,205,778 instructions # 0.80 insn per cycle 40,467,926 branches # 113.732 M/sec 369,002,122 instructions # 0.62 insn per cycle 40,426,145 branches # 189.361 M/sec 369,036,706 instructions # 0.63 insn per cycle 40,430,860 branches # 204.105 M/sec [..] NEW API =3D=3D=3D=3D=3D=3D=3D 3 first results out of 10 265,799,293 instructions # 0.51 insn per cycle 29,834,567 branches # 170.281 M/sec 265,765,970 instructions # 0.55 insn per cycle 29,829,019 branches # 161.602 M/sec 265,764,702 instructions # 0.51 insn per cycle 29,828,015 branches # 189.677 M/sec [..] T-test on all 10 runs =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Difference at 95.0% confidence -1.03219e+08 +/- 55308.7 -27.9705% +/- 0.0149878% (Student's t, pooled s =3D 58864.4) The old API will stay around until the remaining users switch to the new one. After that we'll also remove zsmalloc per-CPU buffer and CPU hotplug handling. The split of map(RO) and map(WO) into read_{begin/end}/write is suggested by Yosry Ahmed. Suggested-by: Yosry Ahmed Signed-off-by: Sergey Senozhatsky --- include/linux/zsmalloc.h | 8 +++ mm/zsmalloc.c | 129 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 137 insertions(+) diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h index a48cd0ffe57d..7d70983cf398 100644 --- a/include/linux/zsmalloc.h +++ b/include/linux/zsmalloc.h @@ -58,4 +58,12 @@ unsigned long zs_compact(struct zs_pool *pool); unsigned int zs_lookup_class_index(struct zs_pool *pool, unsigned int size= ); =20 void zs_pool_stats(struct zs_pool *pool, struct zs_pool_stats *stats); + +void *zs_obj_read_begin(struct zs_pool *pool, unsigned long handle, + void *local_copy); +void zs_obj_read_end(struct zs_pool *pool, unsigned long handle, + void *handle_mem); +void zs_obj_write(struct zs_pool *pool, unsigned long handle, + void *handle_mem, size_t mem_len); + #endif diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 03710d71d022..1288a4120855 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1377,6 +1377,135 @@ void zs_unmap_object(struct zs_pool *pool, unsigned= long handle) } EXPORT_SYMBOL_GPL(zs_unmap_object); =20 +void *zs_obj_read_begin(struct zs_pool *pool, unsigned long handle, + void *local_copy) +{ + struct zspage *zspage; + struct zpdesc *zpdesc; + unsigned long obj, off; + unsigned int obj_idx; + struct size_class *class; + void *addr; + + WARN_ON(in_interrupt()); + + /* Guarantee we can get zspage from handle safely */ + read_lock(&pool->lock); + obj =3D handle_to_obj(handle); + obj_to_location(obj, &zpdesc, &obj_idx); + zspage =3D get_zspage(zpdesc); + + /* Make sure migration doesn't move any pages in this zspage */ + zspage_read_lock(zspage); + read_unlock(&pool->lock); + + class =3D zspage_class(pool, zspage); + off =3D offset_in_page(class->size * obj_idx); + + if (off + class->size <=3D PAGE_SIZE) { + /* this object is contained entirely within a page */ + addr =3D kmap_local_zpdesc(zpdesc); + addr +=3D off; + } else { + size_t sizes[2]; + + /* this object spans two pages */ + sizes[0] =3D PAGE_SIZE - off; + sizes[1] =3D class->size - sizes[0]; + addr =3D local_copy; + + memcpy_from_page(addr, zpdesc_page(zpdesc), + off, sizes[0]); + zpdesc =3D get_next_zpdesc(zpdesc); + memcpy_from_page(addr + sizes[0], + zpdesc_page(zpdesc), + 0, sizes[1]); + } + + if (!ZsHugePage(zspage)) + addr +=3D ZS_HANDLE_SIZE; + + return addr; +} +EXPORT_SYMBOL_GPL(zs_obj_read_begin); + +void zs_obj_read_end(struct zs_pool *pool, unsigned long handle, + void *handle_mem) +{ + struct zspage *zspage; + struct zpdesc *zpdesc; + unsigned long obj, off; + unsigned int obj_idx; + struct size_class *class; + + obj =3D handle_to_obj(handle); + obj_to_location(obj, &zpdesc, &obj_idx); + zspage =3D get_zspage(zpdesc); + class =3D zspage_class(pool, zspage); + off =3D offset_in_page(class->size * obj_idx); + + if (off + class->size <=3D PAGE_SIZE) { + if (!ZsHugePage(zspage)) + off +=3D ZS_HANDLE_SIZE; + handle_mem -=3D off; + kunmap_local(handle_mem); + } + + zspage_read_unlock(zspage); +} +EXPORT_SYMBOL_GPL(zs_obj_read_end); + +void zs_obj_write(struct zs_pool *pool, unsigned long handle, + void *handle_mem, size_t mem_len) +{ + struct zspage *zspage; + struct zpdesc *zpdesc; + unsigned long obj, off; + unsigned int obj_idx; + struct size_class *class; + + WARN_ON(in_interrupt()); + + /* Guarantee we can get zspage from handle safely */ + read_lock(&pool->lock); + obj =3D handle_to_obj(handle); + obj_to_location(obj, &zpdesc, &obj_idx); + zspage =3D get_zspage(zpdesc); + + /* Make sure migration doesn't move any pages in this zspage */ + zspage_read_lock(zspage); + read_unlock(&pool->lock); + + class =3D zspage_class(pool, zspage); + off =3D offset_in_page(class->size * obj_idx); + + if (off + class->size <=3D PAGE_SIZE) { + /* this object is contained entirely within a page */ + void *dst =3D kmap_local_zpdesc(zpdesc); + + if (!ZsHugePage(zspage)) + off +=3D ZS_HANDLE_SIZE; + memcpy(dst + off, handle_mem, mem_len); + kunmap_local(dst); + } else { + /* this object spans two pages */ + size_t sizes[2]; + + off +=3D ZS_HANDLE_SIZE; + sizes[0] =3D PAGE_SIZE - off; + sizes[1] =3D mem_len - sizes[0]; + + memcpy_to_page(zpdesc_page(zpdesc), off, + handle_mem, sizes[0]); 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Fri, 21 Feb 2025 14:31:20 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v8 13/17] zram: switch to new zsmalloc object mapping API Date: Sat, 22 Feb 2025 07:25:44 +0900 Message-ID: <20250221222958.2225035-14-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <20250221222958.2225035-1-senozhatsky@chromium.org> References: <20250221222958.2225035-1-senozhatsky@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Use new read/write zsmalloc object API. For cases when RO mapped object spans two physical pages (requires temp buffer) compression streams now carry around one extra physical page. Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zcomp.c | 4 +++- drivers/block/zram/zcomp.h | 2 ++ drivers/block/zram/zram_drv.c | 28 ++++++++++------------------ 3 files changed, 15 insertions(+), 19 deletions(-) diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c index cfdde2e0748a..a1d627054bb1 100644 --- a/drivers/block/zram/zcomp.c +++ b/drivers/block/zram/zcomp.c @@ -45,6 +45,7 @@ static const struct zcomp_ops *backends[] =3D { static void zcomp_strm_free(struct zcomp *comp, struct zcomp_strm *zstrm) { comp->ops->destroy_ctx(&zstrm->ctx); + vfree(zstrm->local_copy); vfree(zstrm->buffer); zstrm->buffer =3D NULL; } @@ -57,12 +58,13 @@ static int zcomp_strm_init(struct zcomp *comp, struct z= comp_strm *zstrm) if (ret) return ret; =20 + zstrm->local_copy =3D vzalloc(PAGE_SIZE); /* * allocate 2 pages. 1 for compressed data, plus 1 extra for the * case when compressed size is larger than the original one */ zstrm->buffer =3D vzalloc(2 * PAGE_SIZE); - if (!zstrm->buffer) { + if (!zstrm->buffer || !zstrm->local_copy) { zcomp_strm_free(comp, zstrm); return -ENOMEM; } diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h index 23b8236b9090..25339ed1e07e 100644 --- a/drivers/block/zram/zcomp.h +++ b/drivers/block/zram/zcomp.h @@ -34,6 +34,8 @@ struct zcomp_strm { struct mutex lock; /* compression buffer */ void *buffer; + /* local copy of handle memory */ + void *local_copy; struct zcomp_ctx ctx; }; =20 diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index b96be8576cbc..1ce981ce6f48 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1566,11 +1566,11 @@ static int read_incompressible_page(struct zram *zr= am, struct page *page, void *src, *dst; =20 handle =3D zram_get_handle(zram, index); - src =3D zs_map_object(zram->mem_pool, handle, ZS_MM_RO); + src =3D zs_obj_read_begin(zram->mem_pool, handle, NULL); dst =3D kmap_local_page(page); copy_page(dst, src); kunmap_local(dst); - zs_unmap_object(zram->mem_pool, handle); + zs_obj_read_end(zram->mem_pool, handle, src); =20 return 0; } @@ -1588,11 +1588,11 @@ static int read_compressed_page(struct zram *zram, = struct page *page, u32 index) prio =3D zram_get_priority(zram, index); =20 zstrm =3D zcomp_stream_get(zram->comps[prio]); - src =3D zs_map_object(zram->mem_pool, handle, ZS_MM_RO); + src =3D zs_obj_read_begin(zram->mem_pool, handle, zstrm->local_copy); dst =3D kmap_local_page(page); ret =3D zcomp_decompress(zram->comps[prio], zstrm, src, size, dst); kunmap_local(dst); - zs_unmap_object(zram->mem_pool, handle); + zs_obj_read_end(zram->mem_pool, handle, src); zcomp_stream_put(zstrm); =20 return ret; @@ -1688,7 +1688,7 @@ static int write_incompressible_page(struct zram *zra= m, struct page *page, u32 index) { unsigned long handle; - void *src, *dst; + void *src; =20 /* * This function is called from preemptible context so we don't need @@ -1705,11 +1705,9 @@ static int write_incompressible_page(struct zram *zr= am, struct page *page, return -ENOMEM; } =20 - dst =3D zs_map_object(zram->mem_pool, handle, ZS_MM_WO); src =3D kmap_local_page(page); - memcpy(dst, src, PAGE_SIZE); + zs_obj_write(zram->mem_pool, handle, src, PAGE_SIZE); kunmap_local(src); - zs_unmap_object(zram->mem_pool, handle); =20 zram_slot_lock(zram, index); zram_set_flag(zram, index, ZRAM_HUGE); @@ -1730,7 +1728,7 @@ static int zram_write_page(struct zram *zram, struct = page *page, u32 index) int ret =3D 0; unsigned long handle; unsigned int comp_len; - void *dst, *mem; + void *mem; struct zcomp_strm *zstrm; unsigned long element; bool same_filled; @@ -1776,11 +1774,8 @@ static int zram_write_page(struct zram *zram, struct= page *page, u32 index) return -ENOMEM; } =20 - dst =3D zs_map_object(zram->mem_pool, handle, ZS_MM_WO); - - memcpy(dst, zstrm->buffer, comp_len); + zs_obj_write(zram->mem_pool, handle, zstrm->buffer, comp_len); zcomp_stream_put(zstrm); - zs_unmap_object(zram->mem_pool, handle); =20 zram_slot_lock(zram, index); zram_set_handle(zram, index, handle); @@ -1892,7 +1887,7 @@ static int recompress_slot(struct zram *zram, u32 ind= ex, struct page *page, unsigned int comp_len_new; 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charset="utf-8" When configured with pre-trained compression/decompression dictionary support, zstd requires custom memory allocator, which it calls internally from compression()/decompression() routines. That means allocation from atomic context (either under entry spin-lock, or per-CPU local-lock or both). Now, with non-atomic zram read()/write(), those limitations are relaxed and we can allow direct and indirect reclaim. Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/backend_zstd.c | 11 +++-------- 1 file changed, 3 insertions(+), 8 deletions(-) diff --git a/drivers/block/zram/backend_zstd.c b/drivers/block/zram/backend= _zstd.c index 1184c0036f44..53431251ea62 100644 --- a/drivers/block/zram/backend_zstd.c +++ b/drivers/block/zram/backend_zstd.c @@ -24,19 +24,14 @@ struct zstd_params { /* * For C/D dictionaries we need to provide zstd with zstd_custom_mem, * which zstd uses internally to allocate/free memory when needed. - * - * This means that allocator.customAlloc() can be called from zcomp_compre= ss() - * under local-lock (per-CPU compression stream), in which case we must use - * GFP_ATOMIC. - * - * Another complication here is that we can be configured as a swap device. */ static void *zstd_custom_alloc(void *opaque, size_t size) { - if (!preemptible()) + /* Technically this should not happen */ + if (WARN_ON_ONCE(!preemptible())) return kvzalloc(size, GFP_ATOMIC); =20 - return kvzalloc(size, __GFP_KSWAPD_RECLAIM | __GFP_NOWARN); 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Fri, 21 Feb 2025 14:31:32 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v8 15/17] zram: do not leak page on recompress_store error path Date: Sat, 22 Feb 2025 07:25:46 +0900 Message-ID: <20250221222958.2225035-16-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <20250221222958.2225035-1-senozhatsky@chromium.org> References: <20250221222958.2225035-1-senozhatsky@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Ensure the page used for local object data is freed on error out path. Fixes: 3f909a60cec1 ("zram: rework recompress target selection strategy") Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zram_drv.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 1ce981ce6f48..1da329cae8ce 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -2022,7 +2022,7 @@ static ssize_t recompress_store(struct device *dev, struct zram_pp_slot *pps; u32 mode =3D 0, threshold =3D 0; u32 prio, prio_max; - struct page *page; + struct page *page =3D NULL; ssize_t ret; =20 prio =3D ZRAM_SECONDARY_COMP; @@ -2166,9 +2166,9 @@ static ssize_t recompress_store(struct device *dev, cond_resched(); } =20 - __free_page(page); - release_init_lock: + if (page) + __free_page(page); release_pp_ctl(zram, ctl); atomic_set(&zram->pp_in_progress, 0); up_read(&zram->init_lock); --=20 2.48.1.601.g30ceb7b040-goog From nobody Tue Dec 16 19:46:24 2025 Received: from mail-pl1-f170.google.com (mail-pl1-f170.google.com [209.85.214.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 27B06254AEC for ; 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charset="utf-8" Ensure the page used for local object data is freed on error out path. Fixes: 330edc2bc059 (zram: rework writeback target selection strategy) Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zram_drv.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 1da329cae8ce..4e9381b153da 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -792,7 +792,7 @@ static ssize_t writeback_store(struct device *dev, unsigned long index =3D 0; struct bio bio; struct bio_vec bio_vec; - struct page *page; + struct page *page =3D NULL; ssize_t ret =3D len; int mode, err; unsigned long blk_idx =3D 0; @@ -934,8 +934,10 @@ static ssize_t writeback_store(struct device *dev, =20 if (blk_idx) free_block_bdev(zram, blk_idx); - __free_page(page); + release_init_lock: + if (page) + __free_page(page); release_pp_ctl(zram, ctl); atomic_set(&zram->pp_in_progress, 0); up_read(&zram->init_lock); --=20 2.48.1.601.g30ceb7b040-goog From nobody Tue Dec 16 19:46:24 2025 Received: from mail-pl1-f179.google.com (mail-pl1-f179.google.com [209.85.214.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 86B08204599 for ; 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charset="utf-8" Explicitly state that zcomp compress/decompress must be called from non-atomic context. Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zcomp.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c index a1d627054bb1..d26a58c67e95 100644 --- a/drivers/block/zram/zcomp.c +++ b/drivers/block/zram/zcomp.c @@ -146,6 +146,7 @@ int zcomp_compress(struct zcomp *comp, struct zcomp_str= m *zstrm, }; int ret; =20 + might_sleep(); ret =3D comp->ops->compress(comp->params, &zstrm->ctx, &req); if (!ret) *dst_len =3D req.dst_len; @@ -162,6 +163,7 @@ int zcomp_decompress(struct zcomp *comp, struct zcomp_s= trm *zstrm, .dst_len =3D PAGE_SIZE, }; =20 + might_sleep(); return comp->ops->decompress(comp->params, &zstrm->ctx, &req); } =20 --=20 2.48.1.601.g30ceb7b040-goog