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Tue, 11 Feb 2025 22:32:11 -0800 (PST) Received: from localhost ([2401:fa00:8f:203:69f5:6852:451e:8142]) by smtp.gmail.com with UTF8SMTPSA id d9443c01a7336-21f93c7e363sm48246805ad.94.2025.02.11.22.32.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Feb 2025 22:32:11 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Kairui Song , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v5 02/18] zram: permit preemption with active compression stream Date: Wed, 12 Feb 2025 15:27:00 +0900 Message-ID: <20250212063153.179231-3-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.502.g6dc24dfdaf-goog In-Reply-To: <20250212063153.179231-1-senozhatsky@chromium.org> References: <20250212063153.179231-1-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 --- drivers/block/zram/zcomp.c | 36 +++++++++++++++++++++++++---------- drivers/block/zram/zcomp.h | 6 +++--- drivers/block/zram/zram_drv.c | 20 +++++++++---------- 3 files changed, 39 insertions(+), 23 deletions(-) diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c index bb514403e305..e83dd9a80a81 100644 --- a/drivers/block/zram/zcomp.c +++ b/drivers/block/zram/zcomp.c @@ -7,6 +7,7 @@ #include #include #include +#include #include #include =20 @@ -54,6 +55,7 @@ static int zcomp_strm_init(struct zcomp *comp, struct zco= mp_strm *zstrm) { int ret; =20 + mutex_init(&zstrm->lock); ret =3D comp->ops->create_ctx(comp->params, &zstrm->ctx); if (ret) return ret; @@ -109,13 +111,29 @@ 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 + * to 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 +169,9 @@ 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"); @@ -166,10 +181,11 @@ 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 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 3708436f1d1f..43f460a45e3e 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1608,7 +1608,7 @@ 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; } @@ -1769,14 +1769,14 @@ 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 @@ -1800,7 +1800,7 @@ 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 | @@ -1812,7 +1812,7 @@ 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; } @@ -1820,7 +1820,7 @@ 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); @@ -1979,7 +1979,7 @@ 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 @@ -1989,7 +1989,7 @@ 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 @@ -2047,13 +2047,13 @@ 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 2.48.1.502.g6dc24dfdaf-goog