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Mon, 10 Aug 2026 19:28:19 -0700 (PDT) Received: from google.com ([2a00:79e0:2031:6:ddfb:e755:8f7f:81af]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-84f5a51f192sm4499377b3a.30.2026.08.10.19.28.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Aug 2026 19:28:19 -0700 (PDT) Date: Tue, 11 Aug 2026 11:28:15 +0900 From: Sergey Senozhatsky To: Longlong Xia Cc: minchan@kernel.org, senozhatsky@chromium.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Longlong Xia , stable@vger.kernel.org Subject: Re: [PATCH 1/1] zsmalloc: account for handle size in class lookup Message-ID: References: <20260809115518.3791787-1-xialonglong2025@163.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=us-ascii Content-Disposition: inline In-Reply-To: <20260809115518.3791787-1-xialonglong2025@163.com> On (26/08/09 19:55), Longlong Xia wrote: > zs_lookup_class_index() lets zram recompression decide whether a newly > compressed object would use a smaller size class. It currently classifies > the payload size directly, while zs_malloc() adds ZS_HANDLE_SIZE before > selecting the class. > > This makes lookup disagree with allocation near size-class boundaries. > With 4 KiB pages, CONFIG_ZSMALLOC_CHAIN_SIZE=8, and 64-bit handles, a > 1025-to-1024-byte recompression appears to move from class 64 to class 62 > although both allocations use class 64. Conversely, a 1049-to-1025-byte > recompression appears to stay in class 64 although the allocations move > from class 65 to class 64. > > As a result, zram can accept replacements with no allocation benefit or > reject ones that would save memory, potentially marking the object > incompressible. > > Factor size-class selection into lookup_size_class(), account for the > handle there, and use the helper for both lookup and allocation. > > Fixes: 7c2af309abd2 ("zram: add size class equals check into recompression") > Assisted-by: Codex:gpt-5.6-sol > Cc: stable@vger.kernel.org > Signed-off-by: Longlong Xia Reviewed-by: Sergey Senozhatsky