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Thu, 27 Oct 2022 12:29:49 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id M7RMJ715WmOGSAAAMHmgww (envelope-from ); Thu, 27 Oct 2022 12:29:49 +0000 Date: Thu, 27 Oct 2022 14:29:49 +0200 From: Michal Hocko To: "Huang, Ying" Cc: Feng Tang , Aneesh Kumar K V , Andrew Morton , Johannes Weiner , Tejun Heo , Zefan Li , Waiman Long , "linux-mm@kvack.org" , "cgroups@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Hansen, Dave" , "Chen, Tim C" , "Yin, Fengwei" Subject: Re: [PATCH] mm/vmscan: respect cpuset policy during page demotion Message-ID: References: <87wn8lkbk5.fsf@yhuang6-desk2.ccr.corp.intel.com> <87o7txk963.fsf@yhuang6-desk2.ccr.corp.intel.com> <87fsf9k3yg.fsf@yhuang6-desk2.ccr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87fsf9k3yg.fsf@yhuang6-desk2.ccr.corp.intel.com> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666873791; a=rsa-sha256; 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dkim=pass header.d=suse.com header.s=susede1 header.b=RJeUztS7; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf03.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mhocko@suse.com X-Rspamd-Server: rspam11 X-Stat-Signature: iasb11exh4xyhhzqahb93oocc1wcx9p4 X-Rspamd-Queue-Id: 92DF720030 X-HE-Tag: 1666873791-731753 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 Thu 27-10-22 17:31:35, Huang, Ying wrote: > Michal Hocko writes: > > > On Thu 27-10-22 15:39:00, Huang, Ying wrote: > >> Michal Hocko writes: > >> > >> > On Thu 27-10-22 14:47:22, Huang, Ying wrote: > >> >> Michal Hocko writes: > >> > [...] > >> >> > I can imagine workloads which wouldn't like to get their memory demoted > >> >> > for some reason but wouldn't it be more practical to tell that > >> >> > explicitly (e.g. via prctl) rather than configuring cpusets/memory > >> >> > policies explicitly? > >> >> > >> >> If my understanding were correct, prctl() configures the process or > >> >> thread. > >> > > >> > Not necessarily. There are properties which are per adddress space like > >> > PR_[GS]ET_THP_DISABLE. This could be very similar. > >> > > >> >> How can we get process/thread configuration at demotion time? > >> > > >> > As already pointed out in previous emails. You could hook into > >> > folio_check_references path, more specifically folio_referenced_one > >> > where you have all that you need already - all vmas mapping the page and > >> > then it is trivial to get the corresponding vm_mm. If at least one of > >> > them has the flag set then the demotion is not allowed (essentially the > >> > same model as VM_LOCKED). > >> > >> Got it! Thanks for detailed explanation. > >> > >> One bit may be not sufficient. For example, if we want to avoid or > >> control cross-socket demotion and still allow demoting to slow memory > >> nodes in local socket, we need to specify a node mask to exclude some > >> NUMA nodes from demotion targets. > > > > Isn't this something to be configured on the demotion topology side? Or > > do you expect there will be per process/address space usecases? I mean > > different processes running on the same topology, one requesting local > > demotion while other ok with the whole demotion topology? > > I think that it's possible for different processes have different > requirements. > > - Some processes don't care about where the memory is placed, prefer > local, then fall back to remote if no free space. > > - Some processes want to avoid cross-socket traffic, bind to nodes of > local socket. > > - Some processes want to avoid to use slow memory, bind to fast memory > node only. Yes, I do understand that. Do you have any specific examples in mind? [...] > > If we really need/want to give a fine grained control over demotion > > nodemask then we would have to go with vma->mempolicy interface. In > > any case a per process on/off knob sounds like a reasonable first step > > before we learn more about real usecases. > > Yes. Per-mm or per-vma property is much better than per-task property. > Another possibility, how about add a new flag to set_mempolicy() system > call to set the per-mm mempolicy? `numactl` can use that by default. Do you mean a flag to control whether the given policy is applied to a task or mm? -- Michal Hocko SUSE Labs