From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C5B02C32750 for ; Tue, 13 Aug 2019 09:14:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7DADE20663 for ; Tue, 13 Aug 2019 09:14:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7DADE20663 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 2702C6B026B; Tue, 13 Aug 2019 05:14:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 228766B026C; Tue, 13 Aug 2019 05:14:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 136166B026D; Tue, 13 Aug 2019 05:14:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0202.hostedemail.com [216.40.44.202]) by kanga.kvack.org (Postfix) with ESMTP id E69216B026B for ; Tue, 13 Aug 2019 05:14:34 -0400 (EDT) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id 9CE9652AB for ; Tue, 13 Aug 2019 09:14:34 +0000 (UTC) X-FDA: 75816844068.14.tooth96_621a32689cc1a X-HE-Tag: tooth96_621a32689cc1a X-Filterd-Recvd-Size: 6097 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf40.hostedemail.com (Postfix) with ESMTP for ; Tue, 13 Aug 2019 09:14:34 +0000 (UTC) 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 117B6AB91; Tue, 13 Aug 2019 09:14:32 +0000 (UTC) Date: Tue, 13 Aug 2019 11:14:30 +0200 From: Michal Hocko To: Joel Fernandes Cc: Andrew Morton , linux-kernel@vger.kernel.org, Alexey Dobriyan , 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, Robin Murphy , Roman Gushchin , Stephen Rothwell , surenb@google.com, Thomas Gleixner , tkjos@google.com, Vladimir Davydov , Vlastimil Babka , Will Deacon Subject: Re: [PATCH v5 1/6] mm/page_idle: Add per-pid idle page tracking using virtual index Message-ID: <20190813091430.GE17933@dhcp22.suse.cz> References: <20190807171559.182301-1-joel@joelfernandes.org> <20190807130402.49c9ea8bf144d2f83bfeb353@linux-foundation.org> <20190807204530.GB90900@google.com> <20190807135840.92b852e980a9593fe91fbf59@linux-foundation.org> <20190807213105.GA14622@google.com> <20190808080044.GA18351@dhcp22.suse.cz> <20190812145620.GB224541@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190812145620.GB224541@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 Mon 12-08-19 10:56:20, Joel Fernandes wrote: > On Thu, Aug 08, 2019 at 10:00:44AM +0200, Michal Hocko wrote: > > On Wed 07-08-19 17:31:05, Joel Fernandes wrote: > > > On Wed, Aug 07, 2019 at 01:58:40PM -0700, Andrew Morton wrote: > > > > On Wed, 7 Aug 2019 16:45:30 -0400 Joel Fernandes wrote: > > > > > > > > > On Wed, Aug 07, 2019 at 01:04:02PM -0700, Andrew Morton wrote: > > > > > > On Wed, 7 Aug 2019 13:15:54 -0400 "Joel Fernandes (Google)" wrote: > > > > > > > > > > > > > In Android, we are using this for the heap profiler (heapprofd) which > > > > > > > profiles and pin points code paths which allocates and leaves memory > > > > > > > idle for long periods of time. This method solves the security issue > > > > > > > with userspace learning the PFN, and while at it is also shown to yield > > > > > > > better results than the pagemap lookup, the theory being that the window > > > > > > > where the address space can change is reduced by eliminating the > > > > > > > intermediate pagemap look up stage. In virtual address indexing, the > > > > > > > process's mmap_sem is held for the duration of the access. > > > > > > > > > > > > So is heapprofd a developer-only thing? Is heapprofd included in > > > > > > end-user android loads? If not then, again, wouldn't it be better to > > > > > > make the feature Kconfigurable so that Android developers can enable it > > > > > > during development then disable it for production kernels? > > > > > > > > > > Almost all of this code is already configurable with > > > > > CONFIG_IDLE_PAGE_TRACKING. If you disable it, then all of this code gets > > > > > disabled. > > > > > > > > > > Or are you referring to something else that needs to be made configurable? > > > > > > > > Yes - the 300+ lines of code which this patchset adds! > > > > > > > > The impacted people will be those who use the existing > > > > idle-page-tracking feature but who will not use the new feature. I > > > > guess we can assume this set is small... > > > > > > Yes, I think this set should be small. The code size increase of page_idle.o > > > is from ~1KB to ~2KB. Most of the extra space is consumed by > > > page_idle_proc_generic() function which this patch adds. I don't think adding > > > another CONFIG option to disable this while keeping existing > > > CONFIG_IDLE_PAGE_TRACKING enabled, is worthwhile but I am open to the > > > addition of such an option if anyone feels strongly about it. I believe that > > > once this patch is merged, most like this new interface being added is what > > > will be used more than the old interface (for some of the usecases) so it > > > makes sense to keep it alive with CONFIG_IDLE_PAGE_TRACKING. > > > > I would tend to agree with Joel here. The functionality falls into an > > existing IDLE_PAGE_TRACKING config option quite nicely. If there really > > are users who want to save some space and this is standing in the way > > then they can easily add a new config option with some justification so > > the savings are clear. Without that an additional config simply adds to > > the already existing configurability complexity and balkanization. > > Michal, Andrew, Minchan, > > Would you have any other review comments on the v5 series? This is just a new > interface that does not disrupt existing users of the older page-idle > tracking, so as such it is a safe change (as in, doesn't change existing > functionality except for the draining bug fix). I hope to find some more time to finish the review but let me point out that "it's new it is regression safe" is not really a great argument for a new user visible API. If the API is flawed then this is likely going to kick us later and will be hard to fix. I am still not convinced about the swap part of the thing TBH. -- Michal Hocko SUSE Labs