From 270700dd06ca41a4779c19eb46608f076bb7d40e Mon Sep 17 00:00:00 2001 From: Barry Song Date: Thu, 22 Feb 2024 21:11:35 +1300 Subject: [PATCH] mm/zswap: remove the memcpy if acomp is not sleepable Most compressors are actually CPU-based and won't sleep during compression and decompression. We should remove the redundant memcpy for them. This patch checks if the algorithm is sleepable by testing the CRYPTO_ALG_ASYNC algorithm flag. Generally speaking, async and sleepable are semantically similar but not equal. But for compress drivers, they are basically equal at least due to the below facts. Firstly, scompress drivers - crypto/deflate.c, lz4.c, zstd.c, lzo.c etc have no sleep. Secondly, zRAM has been using these scompress drivers for years in atomic contexts, and never worried those drivers going to sleep. One exception is that an async driver can sometimes still return synchronously per Herbert's clarification. In this case, we are still having a redundant memcpy. But we can't know if one particular acomp request will sleep or not unless crypto can expose more details for each specific request from offload drivers. Link: https://lkml.kernel.org/r/20240222081135.173040-3-21cnbao@gmail.com Signed-off-by: Barry Song Tested-by: Chengming Zhou Reviewed-by: Nhat Pham Acked-by: Yosry Ahmed Reviewed-by: Chengming Zhou Acked-by: Chris Li Acked-by: Johannes Weiner Cc: Dan Streetman Cc: David S. Miller Cc: Herbert Xu Cc: Seth Jennings Cc: Vitaly Wool Signed-off-by: Andrew Morton --- mm/zswap.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/zswap.c b/mm/zswap.c index 9a3237752082..9dec853647c8 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -162,6 +162,7 @@ struct crypto_acomp_ctx { struct crypto_wait wait; u8 *buffer; struct mutex mutex; + bool is_sleepable; }; /* @@ -951,6 +952,7 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node) goto acomp_fail; } acomp_ctx->acomp = acomp; + acomp_ctx->is_sleepable = acomp_is_async(acomp); req = acomp_request_alloc(acomp_ctx->acomp); if (!req) { @@ -1078,7 +1080,7 @@ static void zswap_decompress(struct zswap_entry *entry, struct page *page) mutex_lock(&acomp_ctx->mutex); src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO); - if (!zpool_can_sleep_mapped(zpool)) { + if (acomp_ctx->is_sleepable && !zpool_can_sleep_mapped(zpool)) { memcpy(acomp_ctx->buffer, src, entry->length); src = acomp_ctx->buffer; zpool_unmap_handle(zpool, entry->handle); @@ -1092,7 +1094,7 @@ static void zswap_decompress(struct zswap_entry *entry, struct page *page) BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE); mutex_unlock(&acomp_ctx->mutex); - if (zpool_can_sleep_mapped(zpool)) + if (!acomp_ctx->is_sleepable || zpool_can_sleep_mapped(zpool)) zpool_unmap_handle(zpool, entry->handle); }