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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6BC6AC38A02 for ; Fri, 28 Oct 2022 17:17:06 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EDF1D6B0071; Fri, 28 Oct 2022 13:17:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E8F736B0073; Fri, 28 Oct 2022 13:17:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D57696B0074; Fri, 28 Oct 2022 13:17:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id CA51E6B0071 for ; Fri, 28 Oct 2022 13:17:05 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 479D380657 for ; Fri, 28 Oct 2022 17:17:05 +0000 (UTC) X-FDA: 80071013610.16.034D42B Received: from mail-pg1-f178.google.com (mail-pg1-f178.google.com [209.85.215.178]) by imf26.hostedemail.com (Postfix) with ESMTP id A3DB7140010 for ; Fri, 28 Oct 2022 17:17:04 +0000 (UTC) Received: by mail-pg1-f178.google.com with SMTP id q71so5363062pgq.8 for ; Fri, 28 Oct 2022 10:17:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=p/iFIiIQ4V/YG7z76viQuYS3yb9ejhlzHXVIf3GCB3g=; b=A8GT3O8vI9X19QgBEVf5E/OPc4lfK8HPm3Ew/a9eW0pnni7NeBYGN/DULPE7VIYPgU 8COLbv4fiUgLlvbWvkSLCRHfDiV77xFtFIjjifwEPx46vRJV0xJswjtD8h7GKbi3Rlx2 BFjQaN2GQWxaNjQBQQxy7HS9p4eX45eM1mZUv2Wy7bCXKErkuorc5epRjiYVPAPkzjSq 4jhaUF3y/T8IMdnGR4KqXvRXXIaj9KGe/eUaHTqBz4cmektDnj3a7mloDOomkPWPyh3v VqeK15PZdA0RYo82JNHNXe9zPF2nlSflG8XS6+ejLG1NHAcxDWxd5mGjXtMy/2xgo8CY hlZg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=p/iFIiIQ4V/YG7z76viQuYS3yb9ejhlzHXVIf3GCB3g=; b=EMH9iwfXDp7yAgvoRCG5RfC052Dsio8o/GxoCvHWpUNygEXCuK3d16LWA2L8AmZtTw rUnxxbGNms1y4auN2IXnlFHmK/MgM6EXSUb7jYuRj3K/uIXdSgkoRoNUP5bN020Lb9L1 rZRi+RQr5WgUNdz1uxa3HPYvuJ6RI+6BLcJtOFvRoYfhvzxBgDN9FF1hII/3ft0kdhDE RY6lkgf8mTV2moCF127CwxcU/gUdKvxBT1GEGRFT+lx0zL7FymWPfipj63WtDJM+9buZ ZFRGnMkpnXs1m0QdN2AyK4oAFeSPrVeNkUxaAxHw8YveY/jfcQ/W0SZW9kYCtbXJ+8mG vEAA== X-Gm-Message-State: ACrzQf1waY07AMKihd4dx3OUvKCYDWfe9wNzHZsR7D4dm5KCRsXmsgjk bq0kr5RyFiDAmoivvLtSi/0canXHntBCgWJJChE= X-Google-Smtp-Source: AMsMyM76O004qf5Q1nEkt4XBQVb3BWLSFy4Chj1tPZawp9u8P41jJzxgjw5cAOrp2TMqFZROVn9SzHKoyZ2QW2rhB9I= X-Received: by 2002:a05:6a02:20c:b0:461:74e5:ce9f with SMTP id bh12-20020a056a02020c00b0046174e5ce9fmr493837pgb.294.1666977423378; Fri, 28 Oct 2022 10:17:03 -0700 (PDT) MIME-Version: 1.0 References: <20221026074343.6517-1-feng.tang@intel.com> <7b5f533d-4b2e-b45b-ee42-5e1cc3e8a279@linux.ibm.com> In-Reply-To: <7b5f533d-4b2e-b45b-ee42-5e1cc3e8a279@linux.ibm.com> From: Yang Shi Date: Fri, 28 Oct 2022 10:16:50 -0700 Message-ID: Subject: Re: [PATCH] mm/vmscan: respect cpuset policy during page demotion To: Aneesh Kumar K V Cc: Feng Tang , "Hocko, Michal" , Andrew Morton , Johannes Weiner , Tejun Heo , Zefan Li , Waiman Long , "Huang, Ying" , "linux-mm@kvack.org" , "cgroups@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Hansen, Dave" , "Chen, Tim C" , "Yin, Fengwei" Content-Type: text/plain; charset="UTF-8" ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666977424; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=p/iFIiIQ4V/YG7z76viQuYS3yb9ejhlzHXVIf3GCB3g=; b=gaaKr3aIEXuiiNtiZ2ZyOYka1Zr2qU8dF/797fIMZnEcv9SvqFcvHgLMRHFnEpUgWaRIXv bM1ifqgOg9NUPuxDMj8m93zftKYmWs5sG+dhsIOkKCVtvHOaVURKAkG/keE1BCFMozU14R jcnmF4zk/L4x6guVMRmIPy7Dtx3JJoc= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=A8GT3O8v; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf26.hostedemail.com: domain of shy828301@gmail.com designates 209.85.215.178 as permitted sender) smtp.mailfrom=shy828301@gmail.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666977424; a=rsa-sha256; cv=none; b=357xZeC5fhe04qM4ilS0RNhID14dnBTj23gUzzFTn9pDmrOLD/+baN4hd7l/VdOfq3P7Qe yiYVDRElfVtn03p+nWfJ52zjBB7y1mR0mGYZAF8GF8BF5zllWwZwG5RsWJu0SLXqD6CV4o FUnlfND65I5N4aMjJHbbOlLgwu53Vaw= X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: A3DB7140010 X-Rspam-User: Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=A8GT3O8v; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf26.hostedemail.com: domain of shy828301@gmail.com designates 209.85.215.178 as permitted sender) smtp.mailfrom=shy828301@gmail.com X-Stat-Signature: jjm1mmbs13ycsb78qiznfcwbcq4c3o4y X-HE-Tag: 1666977424-277061 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, Oct 27, 2022 at 10:09 PM Aneesh Kumar K V wrote: > > On 10/27/22 11:25 PM, Yang Shi wrote: > > On Thu, Oct 27, 2022 at 12:12 AM Feng Tang wrote: > >> > >> 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; > >> if (vma->vm_mm) > >> task = vma->vm_mm->owner; > > > > But this task may not be the task you want IIUC. For example, the > > process has two threads, A and B. They have different mempolicy. The > > vmscan is trying to demote a page belonging to thread A, but the task > > may point to thread B, so you actually get the wrong mempolicy IIUC. > > > > But if we swap out this page and fault back in via thread B the page would > get allocated as per thread B mempolicy. So if we demote based on thread B > policy are we breaking anything? If the page is demoted by following thread B's mempolicy, didn't it already break thread A's mempolicy in the first place if you care about it? If thread A and thread B have the same mempolicy, then it is not a problem. Actually there is another problem for shared page. If a page is shared by two processes, P1 and P2, when you do rmap walk to find the task, you may find two contradict mempolicy, what mempolicy would you like to obey? Do you have to save all the intermediate mempolicy results somewhere or you just bail out once the first mempolicy is found? > > -aneesh > >