From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joel Fernandes Subject: Re: [PATCH v4 3/5] [RFC] arm64: Add support for idle bit in swap PTE Date: Tue, 6 Aug 2019 07:26:06 -0400 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 Return-path: Content-Disposition: inline In-Reply-To: <20190806111452.GW11812@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org 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 List-Id: linux-api@vger.kernel.org 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