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[209.85.220.65]) by mx.google.com with SMTPS id go5sor102969488plb.37.2019.08.06.04.26.08 for (Google Transport Security); Tue, 06 Aug 2019 04:26:08 -0700 (PDT) Received-SPF: pass (google.com: domain of joel@joelfernandes.org designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@joelfernandes.org header.s=google header.b=KdWHadNe; spf=pass (google.com: domain of joel@joelfernandes.org designates 209.85.220.65 as permitted sender) smtp.mailfrom=joel@joelfernandes.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=eQDxozI2qjukpUkcofnkYlDLvFKSd1P/XqoYuWp8Iko=; b=KdWHadNeW6pa2dnhFD6vGAJeFuZ4bU94l8h5hGmJoB6iVklb97AFdq2hkigQMM5/UW duwzf5xlAas4hj7F57fOHGW4Fbh0eAqKIwiEUMntWH0rzszBSsXQxg7vmdW0vXnYKvIV u177tjd2FQ7ASDBdqt2QwZ/5p/Ocdpipr0UPw= X-Google-Smtp-Source: APXvYqyhzcoKkLyUNInxKHTRQ0D58ehVR/MM5voEdZBk61kMSmPqKu2JfV8+IDkI8ipd4TE0B17EDQ== X-Received: by 2002:a17:902:a413:: with SMTP id p19mr2767311plq.134.1565090768446; Tue, 06 Aug 2019 04:26:08 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id h14sm113010833pfq.22.2019.08.06.04.26.07 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 06 Aug 2019 04:26:07 -0700 (PDT) Date: Tue, 6 Aug 2019 07:26:06 -0400 From: Joel Fernandes To: Michal Hocko Cc: Minchan Kim , 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: <20190806112606.GC117316@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> <20190806110737.GB32615@google.com> <20190806111452.GW11812@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190806111452.GW11812@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 01:14:52PM +0200, Michal Hocko wrote: > On Tue 06-08-19 20:07:37, Minchan Kim 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? > > > > 1. mark page-A idle which was present at that time. > > 2. run workload > > 3. page-A is touched several times > > 4. *sudden* memory pressure happen so finally page A is finally swapped out > > 5. now see the page A idle - but it's incorrect. > > Could you expand on what you mean by idle exactly? Why pageout doesn't > really qualify as "mark-idle and reclaim"? Also could you describe a > usecase where the swapout distinction really matters and it would lead > to incorrect behavior? Michal, Did you read this post ? : https://lore.kernel.org/lkml/20190806104715.GC218260@google.com/T/#m4ece68ceaf6e54d4d29e974f5f4c1080e733f6c1 Just wanted to be sure you did not miss it. thanks, - Joel