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[101.111.9.128]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70b15417a7bsm971274b3a.205.2024.07.05.19.25.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Jul 2024 19:25:47 -0700 (PDT) From: Takero Funaki To: Johannes Weiner , Yosry Ahmed , Nhat Pham , Chengming Zhou , Jonathan Corbet , Andrew Morton , Domenico Cerasuolo Cc: Takero Funaki , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 5/6] mm: zswap: store incompressible page as-is Date: Sat, 6 Jul 2024 02:25:21 +0000 Message-ID: <20240706022523.1104080-6-flintglass@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240706022523.1104080-1-flintglass@gmail.com> References: <20240706022523.1104080-1-flintglass@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable This patch allows zswap to accept incompressible pages and store them into zpool if possible. This change is required to achieve zero rejection on zswap_store(). With proper amount of proactive shrinking, swapout can be buffered by zswap without IO latency. Storing incompressible pages may seem costly, but it can reduce latency. A rare incompressible page in a large batch of compressive pages can delay the entire batch during swapping. The memory overhead is negligible because the underlying zsmalloc already accepts nearly incompressible=C2=A0pages. zsmalloc stores data close to PAGE_SIZE to a dedicated page. Thus storing as-is saves decompression cycles without allocation overhead.=C2=A0zswap itself has not rejected pages in these cases. To store the page as-is, use the compressed data size field `length` in struct `zswap_entry`. The length =3D=3D PAGE_SIZE indicates incompressible=C2=A0data. If a zpool backend does not support allocating PAGE_SIZE (zbud), the behavior remains unchanged. The allocation failure reported by the zpool blocks accepting the page as before. Signed-off-by: Takero Funaki --- mm/zswap.c | 36 +++++++++++++++++++++++++++++++++--- 1 file changed, 33 insertions(+), 3 deletions(-) diff --git a/mm/zswap.c b/mm/zswap.c index 76691ca7b6a7..def0f948a4ab 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -186,6 +186,8 @@ static struct shrinker *zswap_shrinker; * length - the length in bytes of the compressed page data. Needed during * decompression. For a same value filled page length is 0, and b= oth * pool and lru are invalid and must be ignored. + * If length is equal to PAGE_SIZE, the data stored in handle is + * not compressed. The data must be copied to page as-is. * pool - the zswap_pool the entry's data is in * handle - zpool allocation handle that stores the compressed page data * value - value of the same-value filled pages which have same content @@ -969,9 +971,23 @@ static bool zswap_compress(struct folio *folio, struct= zswap_entry *entry) */ comp_ret =3D crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acom= p_ctx->wait); dlen =3D acomp_ctx->req->dlen; - if (comp_ret) + + /* coa_compress returns -EINVAL for errors including insufficient dlen */ + if (comp_ret && comp_ret !=3D -EINVAL) goto unlock; =20 + /* + * If the data cannot be compressed well, store the data as-is. + * Switching by a threshold at + * PAGE_SIZE - (allocation granularity) + * zbud and z3fold use 64B granularity. + * zsmalloc stores >3632B in one page for 4K page arch. + */ + if (comp_ret || dlen > PAGE_SIZE - 64) { + /* we do not use compressed result anymore */ + comp_ret =3D 0; + dlen =3D PAGE_SIZE; + } zpool =3D zswap_find_zpool(entry); gfp =3D __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM; if (zpool_malloc_support_movable(zpool)) @@ -981,14 +997,20 @@ static bool zswap_compress(struct folio *folio, struc= t zswap_entry *entry) goto unlock; =20 buf =3D zpool_map_handle(zpool, handle, ZPOOL_MM_WO); - memcpy(buf, dst, dlen); + + /* PAGE_SIZE indicates not compressed. */ + if (dlen =3D=3D PAGE_SIZE) + memcpy_from_folio(buf, folio, 0, PAGE_SIZE); + else + memcpy(buf, dst, dlen); + zpool_unmap_handle(zpool, handle); =20 entry->handle =3D handle; entry->length =3D dlen; =20 unlock: - if (comp_ret =3D=3D -ENOSPC || alloc_ret =3D=3D -ENOSPC) + if (alloc_ret =3D=3D -ENOSPC) zswap_reject_compress_poor++; else if (comp_ret) zswap_reject_compress_fail++; @@ -1006,6 +1028,14 @@ static void zswap_decompress(struct zswap_entry *ent= ry, struct page *page) struct crypto_acomp_ctx *acomp_ctx; u8 *src; =20 + if (entry->length =3D=3D PAGE_SIZE) { + /* the content is not compressed. copy back as-is. */ + src =3D zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO); + memcpy_to_page(page, 0, src, entry->length); + zpool_unmap_handle(zpool, entry->handle); + return; + } + acomp_ctx =3D raw_cpu_ptr(entry->pool->acomp_ctx); mutex_lock(&acomp_ctx->mutex); =20 --=20 2.43.0