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[209.85.220.65]) by mx.google.com with SMTPS id s28sor54415957pgl.38.2019.08.06.07.48.01 for (Google Transport Security); Tue, 06 Aug 2019 07:48:01 -0700 (PDT) Received-SPF: pass (google.com: domain of minchan.kim@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=QJ2Cxb8m; spf=pass (google.com: domain of minchan.kim@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=minchan.kim@gmail.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=hPKj1q9pzAw01F3LuwbWC2NJPbuIQVTFZWSZ1tXqf8g=; b=QJ2Cxb8mgxyBmBWFhf+Q6WKHeahBHKbgCHhSNQaP7XebbA7RxANJ+gPXMpYWZCcMSu X359Nf5xHy+rw4UZX4hMjsVID68kwhu4AqXw7NM/rCH4HqG+ZDOo5A5SAswJAMLlEJK8 z7yFfZyf/V+gepSBrVsmRbdzILbhwZtR1o1W4fb6SKsWY3NHkX3qpRxDA2HxO6BGES9y 7Qu4NWlphGVXGI6g6CukvGsD2JQ+Nz4GEb7FiYPGqmYJMTe0BmSKOTXNkgyOg7WD/Aw6 4M1QqWSg1xq7Cal5OUE8Rp+Rt9jVJd04zrvUG6ifgzm+idylAD6YNxfXOLHqgvOdlUn2 Iq4w== X-Google-Smtp-Source: APXvYqykjh8W3ip+qMmEJ9I/374nqTdJG5EsvPbtew94zlKNiZ7NYnx4nG7TA1fgWOgH43oAutyB7w== X-Received: by 2002:a63:1b56:: with SMTP id b22mr3320797pgm.265.1565102881165; Tue, 06 Aug 2019 07:48:01 -0700 (PDT) Received: from google.com ([122.38.223.241]) by smtp.gmail.com with ESMTPSA id r12sm72175100pgb.73.2019.08.06.07.47.50 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 06 Aug 2019 07:47:59 -0700 (PDT) Date: Tue, 6 Aug 2019 23:47:47 +0900 From: Minchan Kim To: Michal Hocko Cc: Joel Fernandes , 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 , 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: <20190806144747.GA72938@google.com> References: <20190805170451.26009-1-joel@joelfernandes.org> <20190805170451.26009-3-joel@joelfernandes.org> <20190806084203.GJ11812@dhcp22.suse.cz> <20190806103627.GA218260@google.com> <20190806104755.GR11812@dhcp22.suse.cz> <20190806111446.GA117316@google.com> <20190806115703.GY11812@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190806115703.GY11812@dhcp22.suse.cz> 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, Aug 06, 2019 at 01:57:03PM +0200, Michal Hocko wrote: > On Tue 06-08-19 07:14:46, Joel Fernandes wrote: > > On Tue, Aug 06, 2019 at 12:47:55PM +0200, Michal Hocko wrote: > > > 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? > > > > That depends on how you think of it. > > I would much prefer to have it documented so that I do not have to guess ;) > > > If you are thinking of a monitoring > > process like a heap profiler, then from the heap profiler's (that only cares > > about the process it is monitoring) perspective it will look extremely odd if > > pages that are recently accessed by the process appear to be idle which would > > falsely look like those processes are leaking memory. The reality being, > > Android forced those pages into swap because of other reasons. I would like > > for the swapping mechanism, whether forced swapping or memory reclaim, not to > > interfere with the idle detection. > > Hmm, but how are you going to handle situation when the page is unmapped > and refaulted again (e.g. a normal reclaim of a pagecache)? You are > losing that information same was as in the swapout case, no? Or am I > missing something? If page is unmapped, it's not a idle memory any longer because it's free memory. We could detect the pte is not present. If page is refaulted, it's not a idle memory any longer because it's accessed again. We could detect it because the newly allocated page doesn't have a PG_idle page flag. Both case, idle page tracking couldn't report them as IDLE so it's okay.