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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=hnwjKeWBS3gGbPLTonrsO/3QESDmxRzIhrG9LgstSBg=; b=I1GYqVQm1LaTRfKVZHKh1AQBlsvGcLhh5w8ngi4hDOVOghL77d0KAJP88+XuKfSbsD fMMF9hBDQs8IbS48uGglL1yQKFYnigFPNJ4FLywXQmI3Xy9Xe6nwwF6Qil1NsijuCJcV zupWd2ocZQ3CyqtzbjJbirEati95NwqTbL/68FiE1iz6OTIBAWX2R9J0wlRYV8LsQsCJ n5X5kKEbH7e2G43xBhzhHy0HTnV5temV2HZc22kwrUe0cZ6QaWBSSenc5s7S0cOZOhpw w4PGIt4HMP/9S8CA4ydmezccziUOmHSjXmx5hy9Yx+zClNewsf1mF3Jkv08xjPYqYRTy 6sEA== X-Gm-Message-State: ANoB5pl7523+f151hlQ79ODBp+jus1yHmbouV8GJdgheikrgbzk2j9sq MoHza1O7hP+OAbZyR8ZgiSeX5vbEMpyn/aPUBP8d7A== X-Google-Smtp-Source: AA0mqf44mxItNX5PwT9MTa3hg1zlUCr++yyxhZxDgD0aQCIBH9N+vMHnKh56DdTmLwzu6ryOqzvZ33Tn8sstjnmqriQ= X-Received: by 2002:a25:cb4e:0:b0:6f0:b3ae:6392 with SMTP id b75-20020a25cb4e000000b006f0b3ae6392mr63654400ybg.245.1670459779288; Wed, 07 Dec 2022 16:36:19 -0800 (PST) MIME-Version: 1.0 References: <20221206171340.139790-1-hannes@cmpxchg.org> <20221206171340.139790-2-hannes@cmpxchg.org> In-Reply-To: <20221206171340.139790-2-hannes@cmpxchg.org> From: Shakeel Butt Date: Wed, 7 Dec 2022 16:36:07 -0800 Message-ID: Subject: Re: [PATCH 1/3] mm: memcontrol: skip moving non-present pages that are mapped elsewhere To: Johannes Weiner Cc: Andrew Morton , Linus Torvalds , Hugh Dickins , Michal Hocko , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 40ABCC0005 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: zjskbcebydfodqhrdeqi1i3erpg1uqtk X-HE-Tag: 1670459779-541416 X-HE-Meta: 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 Wj6dneC1 GBGfSko1UzDAoUg8= 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: On Tue, Dec 6, 2022 at 9:14 AM Johannes Weiner wrote: > > During charge moving, the pte lock and the page lock cover nearly all > cases of stabilizing page_mapped(). The only exception is when we're > looking at a non-present pte and find a page in the page cache or in > the swapcache: if the page is mapped elsewhere, it can become unmapped > outside of our control. For this reason, rmap needs lock_page_memcg(). > > We don't like cgroup-specific locks in generic MM code - especially in > performance-critical MM code - and for a legacy feature that's > unlikely to have many users left - if any. > > So remove the exception. Arguably that's better semantics anyway: the > page is shared, and another process seems to be the more active user. > > Once we stop moving such pages, rmap doesn't need lock_page_memcg() > anymore. The next patch will remove it. > > Suggested-by: Hugh Dickins > Signed-off-by: Johannes Weiner Acked-by: Shakeel Butt