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Sun, 30 Nov 2025 19:56:31 -0800 (PST) Received: from google.com ([2a00:79e0:2031:6:943c:f651:f00f:2459]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29bceb450cfsm106014465ad.74.2025.11.30.19.56.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 30 Nov 2025 19:56:31 -0800 (PST) Date: Mon, 1 Dec 2025 12:56:25 +0900 From: Sergey Senozhatsky To: Barry Song <21cnbao@gmail.com> Cc: Sergey Senozhatsky , Andrew Morton , Richard Chang , Brian Geffon , Minchan Kim , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, Minchan Kim Subject: Re: [PATCH 1/2] zram: introduce compressed data writeback Message-ID: References: <20251128170442.2988502-1-senozhatsky@chromium.org> <20251128170442.2988502-2-senozhatsky@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0CEA0A000A X-Stat-Signature: geobhu5mewxxq6nid6g4f3jif9p6xyqk X-HE-Tag: 1764561392-572078 X-HE-Meta: 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 cJIUCDS4 KQAU4pnitxg35q+tx4uIbcs8n0N+M0wuXcjjTjIc4BiQvbDeujchs8pzaX1oUoX/lUossqXZlsTDHG5a1q2MhL1aZMUVcESjvpyIVhyG4lS6hCzsCUDv2rFcOZKQfiWvcCjr1CFRUg2yfyOdFm4yynjpOZU7DkMiCpLMwH5dVF+Si3sMjlyfB9dPemSAF5qJYrsd/LW6I9FDwOQJ3MewkKGNPdjRTb040KKwp4/HFfCdhR2HWQFDM9ybWe3TqAz1ZJzFaq26bAhYUfRCTDlx+RmQRupvvnYv8haVVN26eGvIcG6+/rDZy1uWNIh8fY2WrjV9FApY/wPXsZ41Umzp2X/ogcuRQj/PcFFq9JUx0egSEB23HjVvFdMhBrDpbwiRY79AwjWLYClyftUs= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Barry, On (25/11/29 17:55), Barry Song wrote: > On Sat, Nov 29, 2025 at 1:06 AM Sergey Senozhatsky > wrote: > > > > From: Richard Chang > > > > Hi Richard, Sergey, > > Thanks a lot for developing this. For years, people have been looking for > compressed data writeback to reduce I/O, such as compacting multiple compressed > blocks into a single page on block devices. I guess this patchset hasn’t reached > that point yet, right? Right. > > zram stores all written back slots raw, which implies that > > during writeback zram first has to decompress slots (except > > for ZRAM_HUGE slots, which are raw already). The problem > > with this approach is that not every written back page gets > > read back (either via read() or via page-fault), which means > > that zram basically wastes CPU cycles and battery decompressing > > such slots. This changes with introduction of decompression > > If a page is swapped out and never read again, does that actually indicate > a memory leak in userspace? No, it just means that there is no page-fault on that page. E.g. we swapped out an unused browser tab and never come back to it within the session: e.g. user closed the tab/app, or logged out of session, or rebooted the device, or simply powered off (desktop/laptop).