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[195.135.220.15]) by mx.google.com with ESMTPS id k8si30304397edd.67.2019.08.06.03.47.58 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 06 Aug 2019 03:47:58 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 73D9CAFCC; Tue, 6 Aug 2019 10:47:57 +0000 (UTC) Date: Tue, 6 Aug 2019 12:47:55 +0200 From: Michal Hocko To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, Robin Murphy , Alexey Dobriyan , Andrew Morton , Borislav Petkov , Brendan Gregg , Catalin Marinas , Christian Hansen , dancol@google.com, fmayer@google.com, "H. Peter Anvin" , Ingo Molnar , Jonathan Corbet , Kees Cook , kernel-team@android.com, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Mike Rapoport , minchan@kernel.org, namhyung@google.com, paulmck@linux.ibm.com, Roman Gushchin , Stephen Rothwell , surenb@google.com, Thomas Gleixner , tkjos@google.com, Vladimir Davydov , Vlastimil Babka , Will Deacon Subject: Re: [PATCH v4 3/5] [RFC] arm64: Add support for idle bit in swap PTE Message-ID: <20190806104755.GR11812@dhcp22.suse.cz> References: <20190805170451.26009-1-joel@joelfernandes.org> <20190805170451.26009-3-joel@joelfernandes.org> <20190806084203.GJ11812@dhcp22.suse.cz> <20190806103627.GA218260@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190806103627.GA218260@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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 06-08-19 06:36:27, Joel Fernandes wrote: > On Tue, Aug 06, 2019 at 10:42:03AM +0200, Michal Hocko wrote: > > On Mon 05-08-19 13:04:49, Joel Fernandes (Google) wrote: > > > This bit will be used by idle page tracking code to correctly identify > > > if a page that was swapped out was idle before it got swapped out. > > > Without this PTE bit, we lose information about if a page is idle or not > > > since the page frame gets unmapped. > > > > And why do we need that? Why cannot we simply assume all swapped out > > pages to be idle? They were certainly idle enough to be reclaimed, > > right? Or what does idle actualy mean here? > > Yes, but other than swapping, in Android a page can be forced to be swapped > out as well using the new hints that Minchan is adding? Yes and that is effectivelly making them idle, no? > Also, even if they were idle enough to be swapped, there is a chance that they > were marked as idle and *accessed* before the swapping. Due to swapping, the > "page was accessed since we last marked it as idle" information is lost. I am > able to verify this. > > Idle in this context means the same thing as in page idle tracking terms, the > page was not accessed by userspace since we last marked it as idle (using > /proc//page_idle). Please describe a usecase and why that information might be useful. -- Michal Hocko SUSE Labs