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27 Oct 2022 00:45:55 -0700 X-IronPort-AV: E=McAfee;i="6500,9779,10512"; a="610259267" X-IronPort-AV: E=Sophos;i="5.95,217,1661842800"; d="scan'208";a="610259267" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by orsmga006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Oct 2022 00:45:52 -0700 From: "Huang, Ying" To: Feng Tang Cc: Yang Shi , "Hocko, Michal" , 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 References: <20221026074343.6517-1-feng.tang@intel.com> Date: Thu, 27 Oct 2022 15:45:12 +0800 In-Reply-To: (Feng Tang's message of "Thu, 27 Oct 2022 15:11:53 +0800") Message-ID: <87k04lk8vr.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; 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b=33hk58fCfeVD1KNkM8OFlqtdBphQiP/qorqmDu0enE2+bICXdK0TIYaFvb4qnHHKoYea/c HLVZbeUsDZPZEc9wtfT5Lbznfo1GP3dTVGr2l8C/SvoQw1bjweqbOWRXbC3zCXe58/Eiyd FXmVvmKu2TQXIGItOGLdzeJ5KvCAreM= X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 0ECA34000E X-Rspam-User: Authentication-Results: imf04.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=a7ajIFD+; dmarc=pass (policy=none) header.from=intel.com; spf=pass (imf04.hostedemail.com: domain of ying.huang@intel.com designates 134.134.136.100 as permitted sender) smtp.mailfrom=ying.huang@intel.com X-Stat-Signature: 1b7ebe9us14z1rzepd3g5nopsijkck8z X-HE-Tag: 1666856776-632305 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: Feng Tang writes: > On Thu, Oct 27, 2022 at 01:57:52AM +0800, Yang Shi wrote: >> On Wed, Oct 26, 2022 at 8:59 AM Michal Hocko wrote: > [...] >> > > > This all can get quite expensive so the primary question is, does the >> > > > existing behavior generates any real issues or is this more of an >> > > > correctness exercise? I mean it certainly is not great to demote to an >> > > > incompatible numa node but are there any reasonable configurations when >> > > > the demotion target node is explicitly excluded from memory >> > > > policy/cpuset? >> > > >> > > We haven't got customer report on this, but there are quite some customers >> > > use cpuset to bind some specific memory nodes to a docker (You've helped >> > > us solve a OOM issue in such cases), so I think it's practical to respect >> > > the cpuset semantics as much as we can. >> > >> > Yes, it is definitely better to respect cpusets and all local memory >> > policies. There is no dispute there. The thing is whether this is really >> > worth it. How often would cpusets (or policies in general) go actively >> > against demotion nodes (i.e. exclude those nodes from their allowes node >> > mask)? >> > >> > 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? >> > >> > > Your concern about the expensive cost makes sense! Some raw ideas are: >> > > * if the shrink_folio_list is called by kswapd, the folios come from >> > > the same per-memcg lruvec, so only one check is enough >> > > * if not from kswapd, like called form madvise or DAMON code, we can >> > > save a memcg cache, and if the next folio's memcg is same as the >> > > cache, we reuse its result. And due to the locality, the real >> > > check is rarely performed. >> > >> > memcg is not the expensive part of the thing. You need to get from page >> > -> all vmas::vm_policy -> mm -> task::mempolicy >> >> Yeah, on the same page with Michal. Figuring out mempolicy from page >> seems quite expensive and the correctness can't be guranteed since the >> mempolicy could be set per-thread and the mm->task depends on >> CONFIG_MEMCG so it doesn't work for !CONFIG_MEMCG. > > Yes, you are right. Our "working" psudo code for mem policy looks like > what Michal mentioned, and it can't work for all cases, but try to > enforce it whenever possible: > > static bool __check_mpol_demotion(struct folio *folio, struct vm_area_struct *vma, > unsigned long addr, void *arg) > { > bool *skip_demotion = arg; > struct mempolicy *mpol; > int nid, dnid; > bool ret = true; > > mpol = __get_vma_policy(vma, addr); > if (!mpol) { > struct task_struct *task; task = NULL; > if (vma->vm_mm) > task = vma->vm_mm->owner; > > if (task) { > mpol = get_task_policy(task); > if (mpol) > mpol_get(mpol); > } > } > > if (!mpol) > return ret; > > if (mpol->mode != MPOL_BIND) > goto put_exit; > > nid = folio_nid(folio); > dnid = next_demotion_node(nid); > if (!node_isset(dnid, mpol->nodes)) { > *skip_demotion = true; > ret = false; > } I think that you need to get a node mask instead. Even if !node_isset(dnid, mpol->nodes), you may demote to other node in the node mask. Best Regards, Huang, Ying > > put_exit: > mpol_put(mpol); > return ret; > } > > static unsigned int shrink_page_list(struct list_head *page_list,..) > { > ... > > bool skip_demotion = false; > struct rmap_walk_control rwc = { > .arg = &skip_demotion, > .rmap_one = __check_mpol_demotion, > }; > > /* memory policy check */ > rmap_walk(folio, &rwc); > if (skip_demotion) > goto keep_locked; > } > > And there seems to be no simple solution for getting the memory > policy from a page. > > Thanks, > Feng > >> > >> > -- >> > Michal Hocko >> > SUSE Labs >> > >>