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Wed, 29 Jan 2025 03:45:51 -0800 (PST) Received: from google.com ([2401:fa00:8f:203:d794:9e7a:5186:857e]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-21da3d9cacfsm98202945ad.31.2025.01.29.03.45.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Jan 2025 03:45:51 -0800 (PST) Date: Wed, 29 Jan 2025 20:45:46 +0900 From: Sergey Senozhatsky To: Kenny Cheng Cc: minchan@kernel.org, senozhatsky@chromium.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, c.s.cheng@realtek.com, Andrew Morton , Yosry Ahmed Subject: Re: [PATCH v2] zsmalloc: Fix address alignment in zspage for performance improvement Message-ID: References: <20250129082825.3760555-1-chao.shun.cheng.tw@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250129082825.3760555-1-chao.shun.cheng.tw@gmail.com> X-Rspamd-Queue-Id: ECEB580010 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: s3s7tyerkk5jnjsnmdhiy8zmmmxpb4oe X-HE-Tag: 1738151152-312284 X-HE-Meta: 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 n7HUIbah nMoyEMiX01KXYG95iake8b/ZAU7pQU3tM0pCdru/MRdObNW74YzESifxQhrkejr9AMOrQaj6gMCSphnDSM+qv+VJMyjmEMzpRHiaHTJLW54jySUYpAKEzw/PBbwc51ol1kNSYklzRz1N0ooju7Iq4CCrifplLOMAUOmnIbsSYXEm5UnbhYnYCaCASuQMechxLdj6s9/DPwHmMK1qKU9yw+s8vCOOikXEJVTSCBxP7+xlQE/BLOC3CgE7SEi3gMRCLL3/aOBadCK1C6vtWZSIR5yVx40bV34ieX3AT1mISu/09LWMiZDbwxDyeboZcjoZaNNBZP8iGq0Gvh8NGDv8pcVHDQF/kRAAWtBwyrxk/cBxeT4wxliOchHflS6fVx+nWc0Aa5Ytm5qq7Xwqz+JABC4kzcoilEqoU7b34b2eZAD+OVmo= X-Bogosity: Ham, tests=bogofilter, spamicity=0.014702, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Cc-ing Andrew and Yosry On (25/01/29 16:28), Kenny Cheng wrote: > The zspage consists of multiple objects, each containing a "link struct" > to connect to the next object. The "link struct" is placed at the > beginning of each object. On a 32-bit system, the size of the "link > struct" is 4 bytes, which means the address returned by `zs_map_object` > is always 4-byte aligned. Sorry, you picked a rather unlucky time to patch zsmalloc, as it goes through some intrusive changes. We need to stabilize those changes first. > For better performance, zram compression/decompression is offloaded to > hardware designed by the IC vendor. For example, Realtek's hardware > requires 16-byte alignment. However, due to the 4-byte alignment, > a `memcpy` operation is needed to move data from the 4-byte aligned > address to the 16-byte aligned address, which negatively impacts zram > performance. Hmm, I don't know. If we change zsmalloc to make some H/W happy, how do we make sure that something that is good for Realtek is not "bad" for some other H/W? I'm very unsure about having "vendor-specific" (by the way, is that out-of-tree compression/decompression driver?) changes in zsmalloc.