From 7d4c9629b74ff7ad3b58e57324e235d710e55c21 Mon Sep 17 00:00:00 2001 From: Yosry Ahmed Date: Wed, 5 Mar 2025 06:11:30 +0000 Subject: [PATCH] mm: zswap: use object read/write APIs instead of object mapping APIs Use the new object read/write APIs instead of mapping APIs. On compress side, zpool_obj_write() is more concise and provides exactly what zswap needs to write the compressed object to the zpool, instead of map->copy->unmap. On the decompress side, zpool_obj_read_begin() is sleepable, which allows avoiding the memcpy() for zsmalloc and slightly simplifying the code by: - Avoiding checking if the zpool driver is sleepable, reducing special cases and shrinking the huge comment. - Having a single zpool_obj_read_end() call rather than multiple conditional zpool_unmap_handle() calls. The !virt_addr_valid() case can be removed in the future if the crypto API supports kmap addresses or by using kmap_to_page(), completely eliminating the memcpy() path in zswap_decompress(). This a step toward that. In that spirit, opportunistically make the comment more specific about the kmap case instead of generic non-linear addresses. This is the only case that needs to be handled in practice, and the generic comment makes it seem like a bigger problem that it actually is. Link: https://lkml.kernel.org/r/20250305061134.4105762-3-yosry.ahmed@linux.dev Signed-off-by: Yosry Ahmed Acked-by: Johannes Weiner Acked-by: Nhat Pham Cc: Chengming Zhou Cc: Herbert Xu Cc: Minchan Kim Cc: Peter Zijlstra Cc: Sergey Senozhatsky Cc: Thomas Gleixner Signed-off-by: Andrew Morton --- mm/zswap.c | 33 +++++++++++++-------------------- 1 file changed, 13 insertions(+), 20 deletions(-) diff --git a/mm/zswap.c b/mm/zswap.c index 8a1ded8fa9731..7de54f105d04d 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -930,7 +930,6 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry, unsigned int dlen = PAGE_SIZE; unsigned long handle; struct zpool *zpool; - char *buf; gfp_t gfp; u8 *dst; @@ -972,10 +971,7 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry, if (alloc_ret) goto unlock; - buf = zpool_map_handle(zpool, handle, ZPOOL_MM_WO); - memcpy(buf, dst, dlen); - zpool_unmap_handle(zpool, handle); - + zpool_obj_write(zpool, handle, dst, dlen); entry->handle = handle; entry->length = dlen; @@ -996,24 +992,22 @@ static void zswap_decompress(struct zswap_entry *entry, struct folio *folio) struct zpool *zpool = entry->pool->zpool; struct scatterlist input, output; struct crypto_acomp_ctx *acomp_ctx; - u8 *src; + u8 *src, *obj; acomp_ctx = acomp_ctx_get_cpu_lock(entry->pool); - src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO); + obj = zpool_obj_read_begin(zpool, entry->handle, acomp_ctx->buffer); + /* - * If zpool_map_handle is atomic, we cannot reliably utilize its mapped buffer - * to do crypto_acomp_decompress() which might sleep. In such cases, we must - * resort to copying the buffer to a temporary one. - * Meanwhile, zpool_map_handle() might return a non-linearly mapped buffer, - * such as a kmap address of high memory or even ever a vmap address. - * However, sg_init_one is only equipped to handle linearly mapped low memory. - * In such cases, we also must copy the buffer to a temporary and lowmem one. + * zpool_obj_read_begin() might return a kmap address of highmem when + * acomp_ctx->buffer is not used. However, sg_init_one() does not + * handle highmem addresses, so copy the object to acomp_ctx->buffer. */ - if ((acomp_ctx->is_sleepable && !zpool_can_sleep_mapped(zpool)) || - !virt_addr_valid(src)) { - memcpy(acomp_ctx->buffer, src, entry->length); + if (virt_addr_valid(obj)) { + src = obj; + } else { + WARN_ON_ONCE(obj == acomp_ctx->buffer); + memcpy(acomp_ctx->buffer, obj, entry->length); src = acomp_ctx->buffer; - zpool_unmap_handle(zpool, entry->handle); } sg_init_one(&input, src, entry->length); @@ -1023,8 +1017,7 @@ static void zswap_decompress(struct zswap_entry *entry, struct folio *folio) BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait)); BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE); - if (src != acomp_ctx->buffer) - zpool_unmap_handle(zpool, entry->handle); + zpool_obj_read_end(zpool, entry->handle, obj); acomp_ctx_put_unlock(acomp_ctx); } -- 2.39.5