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Sun, 02 Mar 2025 18:24:45 -0800 (PST) Received: from localhost ([2401:fa00:8f:203:1513:4f61:a4d3:b418]) by smtp.gmail.com with UTF8SMTPSA id d9443c01a7336-223501d5247sm66569735ad.26.2025.03.02.18.24.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 02 Mar 2025 18:24:45 -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 v10 02/19] zram: permit preemption with active compression stream Date: Mon, 3 Mar 2025 11:03:11 +0900 Message-ID: <20250303022425.285971-3-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.711.g2feabab25a-goog In-Reply-To: <20250303022425.285971-1-senozhatsky@chromium.org> References: <20250303022425.285971-1-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" 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 Signed-off-by: Sergey Senozhatsky Reviewed-by: Yosry Ahmed --- 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 70599d41b828..dd669d48ae6f 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1607,7 +1607,7 @@ 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; } @@ -1768,14 +1768,14 @@ 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 @@ -1799,7 +1799,7 @@ 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 | @@ -1811,7 +1811,7 @@ 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; } @@ -1819,7 +1819,7 @@ 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); @@ -1978,7 +1978,7 @@ 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 @@ -1988,7 +1988,7 @@ 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 @@ -2046,13 +2046,13 @@ static int recompress_slot(struct zram *zram, u32 i= ndex, struct page *page, __GFP_HIGHMEM | __GFP_MOVABLE); if (IS_ERR_VALUE(handle_new)) { - zcomp_stream_put(zram->comps[prio]); + zcomp_stream_put(zstrm); return PTR_ERR((void *)handle_new); } =20 dst =3D zs_map_object(zram->mem_pool, handle_new, ZS_MM_WO); memcpy(dst, zstrm->buffer, comp_len_new); - zcomp_stream_put(zram->comps[prio]); + zcomp_stream_put(zstrm); =20 zs_unmap_object(zram->mem_pool, handle_new); =20 --=20 2.48.1.711.g2feabab25a-goog