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=-11.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 064A8C433E0 for ; Sat, 16 May 2020 00:07:00 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9FFD82065C for ; Sat, 16 May 2020 00:06:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="r0AnL5ov" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9FFD82065C Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 0250F8E0003; Fri, 15 May 2020 20:06:59 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F18628E0001; Fri, 15 May 2020 20:06:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DE0938E0003; Fri, 15 May 2020 20:06:58 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0155.hostedemail.com [216.40.44.155]) by kanga.kvack.org (Postfix) with ESMTP id C29508E0001 for ; Fri, 15 May 2020 20:06:58 -0400 (EDT) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 76724824805A for ; Sat, 16 May 2020 00:06:58 +0000 (UTC) X-FDA: 76820641716.27.steam48_59f0904f8553f X-HE-Tag: steam48_59f0904f8553f X-Filterd-Recvd-Size: 8775 Received: from mail-lj1-f195.google.com (mail-lj1-f195.google.com [209.85.208.195]) by imf47.hostedemail.com (Postfix) with ESMTP for ; Sat, 16 May 2020 00:06:57 +0000 (UTC) Received: by mail-lj1-f195.google.com with SMTP id g4so4049814ljl.2 for ; Fri, 15 May 2020 17:06:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=xjOcJ8psemIC/njQ/FR6hvBA3owD/j/88LT4loTH6ow=; b=r0AnL5ov0wH1Z5BckbiP8WqX7vc9IKjluKmNmaaoZ44YPV3yedbwiXkoP5XUpvbPGu xfeUKdvmqvQvm4g4/ul6R/RLRDfSXaD0AmDltu1f5DiCWM/ReoVbpMJKKVzlrFst3caa DwHXapjEqfrP6GqR2UjujYlsFYdxrl+LdTcn1lmzN6wSGJ20i9YPIDJHkzUePbZbLmF6 ZpmVRFnZuTG+RSs9g3eT2yqN1j05UD2QByf6Qv2EHa81L1miET8Q23nFkSJwF9FgWHzJ REZH0jXKFGcYfUY2WN4c9FaTEFKykwI57QTpzGOTl9tV7gwZeeKbfj7vzUiKJRZCOMET gMgg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=xjOcJ8psemIC/njQ/FR6hvBA3owD/j/88LT4loTH6ow=; b=khiMqtRylR70z2O5VZEurzoqi014m62tWuE0/GsUc+ql11eOHDLuvyylIdMn7+cKAq roqEkYPjg7FMFFU9St7MS1hP3BrZ4yqS85PkEY9L1v8JpN4rlqAmqstTq272CDuQeGuR FYCnTZg2+LQRjG0QEcfq4/xji/FHLzWTTcLy2igGr0RCnWF0PQAzRZ4QYuHSaM3KcD81 joz5r0EJQxbERwfLZ/sNrHTulAyuxUCKqSwCUnH7zbpca4xGvWr1I9CzUI6vbfH9ZfTG pvrrlew+Ug07qPD+m+Cmn6rYSXmWyCqPQk/y9jDtuZPtEy8tgpE9Dj3j5qy2TLoGuGqe /HDw== X-Gm-Message-State: AOAM530TQMo1EBPKQz6kLdWpqhcrTg462Vq8TqUzdRELhHHAcam/WTGL jKijcZmySURoQU6HMcugDScqxRiSacvSjpeoJY43Nw== X-Google-Smtp-Source: ABdhPJwasWHcyfPA85DBo++skrRvg3Fx4LuSmQMPy+CoVVIM5iAtz1194VfARiuxgPiXaHFlA5f35gmn2qzpqgQ1LqQ= X-Received: by 2002:a2e:9255:: with SMTP id v21mr3656290ljg.222.1589587615924; Fri, 15 May 2020 17:06:55 -0700 (PDT) MIME-Version: 1.0 References: <20200508170630.94406-1-shakeelb@google.com> <20200508214405.GA226164@cmpxchg.org> <20200515082955.GJ29153@dhcp22.suse.cz> <20200515132421.GC591266@cmpxchg.org> <20200515150026.GA94522@carbon.DHCP.thefacebook.com> <20200515180920.GC94522@carbon.DHCP.thefacebook.com> In-Reply-To: <20200515180920.GC94522@carbon.DHCP.thefacebook.com> From: Shakeel Butt Date: Fri, 15 May 2020 17:06:44 -0700 Message-ID: Subject: Re: [PATCH] memcg: expose root cgroup's memory.stat To: Roman Gushchin Cc: Johannes Weiner , Michal Hocko , Mel Gorman , Andrew Morton , Yafang Shao , Linux MM , Cgroups , LKML Content-Type: text/plain; charset="UTF-8" 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 Fri, May 15, 2020 at 11:09 AM Roman Gushchin wrote: > > On Fri, May 15, 2020 at 10:49:22AM -0700, Shakeel Butt wrote: > > On Fri, May 15, 2020 at 8:00 AM Roman Gushchin wrote: > > > > > > On Fri, May 15, 2020 at 06:44:44AM -0700, Shakeel Butt wrote: > > > > On Fri, May 15, 2020 at 6:24 AM Johannes Weiner wrote: > > > > > > > > > > On Fri, May 15, 2020 at 10:29:55AM +0200, Michal Hocko wrote: > > > > > > On Sat 09-05-20 07:06:38, Shakeel Butt wrote: > > > > > > > On Fri, May 8, 2020 at 2:44 PM Johannes Weiner wrote: > > > > > > > > > > > > > > > > On Fri, May 08, 2020 at 10:06:30AM -0700, Shakeel Butt wrote: > > > > > > > > > One way to measure the efficiency of memory reclaim is to look at the > > > > > > > > > ratio (pgscan+pfrefill)/pgsteal. However at the moment these stats are > > > > > > > > > not updated consistently at the system level and the ratio of these are > > > > > > > > > not very meaningful. The pgsteal and pgscan are updated for only global > > > > > > > > > reclaim while pgrefill gets updated for global as well as cgroup > > > > > > > > > reclaim. > > > > > > > > > > > > > > > > > > Please note that this difference is only for system level vmstats. The > > > > > > > > > cgroup stats returned by memory.stat are actually consistent. The > > > > > > > > > cgroup's pgsteal contains number of reclaimed pages for global as well > > > > > > > > > as cgroup reclaim. So, one way to get the system level stats is to get > > > > > > > > > these stats from root's memory.stat, so, expose memory.stat for the root > > > > > > > > > cgroup. > > > > > > > > > > > > > > > > > > from Johannes Weiner: > > > > > > > > > There are subtle differences between /proc/vmstat and > > > > > > > > > memory.stat, and cgroup-aware code that wants to watch the full > > > > > > > > > hierarchy currently has to know about these intricacies and > > > > > > > > > translate semantics back and forth. > > > > > > > > > > > > Can we have those subtle differences documented please? > > > > > > > > > > > > > > > > > > > > > > > > Generally having the fully recursive memory.stat at the root > > > > > > > > > level could help a broader range of usecases. > > > > > > > > > > > > > > > > The changelog begs the question why we don't just "fix" the > > > > > > > > system-level stats. It may be useful to include the conclusions from > > > > > > > > that discussion, and why there is value in keeping the stats this way. > > > > > > > > > > > > > > > > > > > > > > Right. Andrew, can you please add the following para to the changelog? > > > > > > > > > > > > > > Why not fix the stats by including both the global and cgroup reclaim > > > > > > > activity instead of exposing root cgroup's memory.stat? The reason is > > > > > > > the benefit of having metrics exposing the activity that happens > > > > > > > purely due to machine capacity rather than localized activity that > > > > > > > happens due to the limits throughout the cgroup tree. Additionally > > > > > > > there are userspace tools like sysstat(sar) which reads these stats to > > > > > > > inform about the system level reclaim activity. So, we should not > > > > > > > break such use-cases. > > > > > > > > > > > > > > > > Signed-off-by: Shakeel Butt > > > > > > > > > Suggested-by: Johannes Weiner > > > > > > > > > > > > > > > > Acked-by: Johannes Weiner > > > > > > > > > > > > > > Thanks a lot. > > > > > > > > > > > > I was quite surprised that the patch is so simple TBH. For some reason > > > > > > I've still had memories that we do not account for root memcg (likely > > > > > > because mem_cgroup_is_root(memcg) bail out in the try_charge. But stats > > > > > > are slightly different here. > > > > > > > > > > Yep, we skip the page_counter for root, but keep in mind that cgroup1 > > > > > *does* have a root-level memory.stat, so (for the most part) we've > > > > > been keeping consumer stats for the root level the whole time. > > > > > > > > > > > counters because they are not really all the same. E.g. > > > > > > - mem_cgroup_charge_statistics accounts for each memcg > > > > > > > > > > Yep, that's heritage from cgroup1. > > > > > > > > > > > - memcg_charge_kernel_stack relies on pages being associated with a > > > > > > memcg and that in turn relies on __memcg_kmem_charge_page which bails > > > > > > out on root memcg > > > > > > > > > > You're right. It should only bypass the page_counter, but still set > > > > > page->mem_cgroup = root_mem_cgroup, just like user pages. > > > > > > What about kernel threads? We consider them belonging to the root memory > > > cgroup. Should their memory consumption being considered in root-level stats? > > > > > > I'm not sure we really want it, but I guess we need to document how > > > kernel threads are handled. > > > > > > > What will be the cons of updating root-level stats for kthreads? > > It makes total sense for stacks, but not much for the slab memory. > Because it's really "some part of the total slab memory, which is > accounted on the memcg level". And it comes with some performance > overhead. > > I'm not really opposing any solution, just saying we need to document > what's included into this statistics and what not. > Yes, I agree. I will explore which stats it makes sense and for which it does not.