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Mon, 01 Dec 2025 01:09:43 -0800 (PST) Received: from google.com ([2a00:79e0:2031:6:943c:f651:f00f:2459]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-be4fb24872fsm11628836a12.1.2025.12.01.01.09.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Dec 2025 01:09:43 -0800 (PST) Date: Mon, 1 Dec 2025 18:09:37 +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-Rspamd-Queue-Id: CBCA91C000D X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: r3uq7quyxrha8fwcyxpu57hnb1wqx8wr X-HE-Tag: 1764580184-699659 X-HE-Meta: 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 jx80WSkd GkfjFFkJ6orfr9+CqNBmIsNsHTCkkLQwllqEEzQu/Im3kYkmey6nGHlkMqQirnirQS1Ruef7nU/C9CulA4pTNrJDbOHvlcS8d04LVJfJk8aWCz9XsSVGxrCFeo9WftWqeyD0kWfA7eT/M41Qx5ECxzb8s7tBoUcGT6y4ACdwxfyB11ah53RVPHEm36+tTKc2qvScsi0hHV6Pzc/VSdYRyFU2u95wp0HxWCDR7wAoXbObokUWDHrNjD628XgpyNuQoWkWaCad6giDYGH+0Dfvra9qptTBZ3nwsDJwAWXkv492kyvbSIMkLEGiLJyCV+eg9IWG1xvmMX/ZwY6oSOSX/FG8WyIH1mugWzNABgfaZgKJWYOXOPtGvLgTRjg== 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: On (25/12/01 16:59), Barry Song wrote: > On Mon, Dec 1, 2025 at 11:56 AM Sergey Senozhatsky > wrote: > [...] > > > > 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). > > Thanks, Sergey. That makes sense to me. On Android, users don’t have a > close button, yet apps can still be OOM-killed; those pages are never > swapped in. I see. I suppose on android you still can swipe up and terminate un-needed apps, wouldn't this be the same? Well, apart from that, zram is not android-specific, some distros use it on desktops/laptops as well.