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Mon, 01 Dec 2025 00:59:30 -0800 (PST) MIME-Version: 1.0 References: <20251128170442.2988502-1-senozhatsky@chromium.org> <20251128170442.2988502-2-senozhatsky@chromium.org> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Mon, 1 Dec 2025 16:59:19 +0800 X-Gm-Features: AWmQ_blOS7Nucw2YNUQvfG1rNrEP4YVyGX1irEsw0vGItmVtTPTGRytfhTT1B2o Message-ID: Subject: Re: [PATCH 1/2] zram: introduce compressed data writeback To: Sergey Senozhatsky Cc: Andrew Morton , Richard Chang , Brian Geffon , Minchan Kim , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, Minchan Kim Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: A107820008 X-Stat-Signature: 7oisfc7s1ypphjofb8prwwofnku83xi9 X-Rspam-User: X-HE-Tag: 1764579571-573270 X-HE-Meta: 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 GFtnkFMO K57oYRYxvJSliESf3cohUDS04CKUMdVKtCyzxlEhehuroidfivKd6b4wQhYzNAKqTnkC8SC4vI4CS7WmuE2xxfEtKipvwoP3KY/w9JUVUeVmm2E0Gi03cb+dVJOQ5FQo+9Sq4Apv/8ji533/mzN7PmzTwHgYiwEStjyTXuDzSRyfaZQjGKz94IRkB0SFm59VyXsIOdXMIZtebErObexchVosO+CdAIPambxCbpLpnXCuSt713r93sW6/ehY08blZaL4VBhDGGL4QvocqDyDyNcYh5qlk3Hi2uU7QAzwp4Dcc8tZqnAjXxljjeN3+QsEPBwxmtTzF7VWX8Jf9GlNAoYLn9X74vwb44QkOmDCOJR56Zlbcr9avCgGm17p1GEjp1jD3n 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 Mon, Dec 1, 2025 at 11:56=E2=80=AFAM 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 indic= ate > > 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=E2=80=99t hav= e a close button, yet apps can still be OOM-killed; those pages are never swapped in. Thanks Barry