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=-23.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL autolearn=ham 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 85BA1C433DB for ; Wed, 17 Feb 2021 14:39:50 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0451064E02 for ; Wed, 17 Feb 2021 14:39:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0451064E02 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 92F646B0006; Wed, 17 Feb 2021 09:39:49 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 8DF536B006C; Wed, 17 Feb 2021 09:39:49 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7A6FF6B006E; Wed, 17 Feb 2021 09:39:49 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0070.hostedemail.com [216.40.44.70]) by kanga.kvack.org (Postfix) with ESMTP id 65ADE6B0006 for ; Wed, 17 Feb 2021 09:39:49 -0500 (EST) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 30AFF824805A for ; Wed, 17 Feb 2021 14:39:49 +0000 (UTC) X-FDA: 77828018898.11.stem51_3b170f12764d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin11.hostedemail.com (Postfix) with ESMTP id F20F1180F68A8 for ; Wed, 17 Feb 2021 14:39:48 +0000 (UTC) X-HE-Tag: stem51_3b170f12764d X-Filterd-Recvd-Size: 6701 Received: from mail-lf1-f52.google.com (mail-lf1-f52.google.com [209.85.167.52]) by imf35.hostedemail.com (Postfix) with ESMTP for ; Wed, 17 Feb 2021 14:39:48 +0000 (UTC) Received: by mail-lf1-f52.google.com with SMTP id d24so21816337lfs.8 for ; Wed, 17 Feb 2021 06:39:48 -0800 (PST) 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=6gl9Lo83ig+3r4SImbYtQt6vySMRjFSrOz26uq39p6I=; b=kvF5qvdWbmtuDAi3w2Kg+NNfVsdfwf87iXRY1trRkLcBsxe1I7L9eHwAcMqQjkvBt/ igbGwBJXwuL8LVixBG0H3Ga0WuVgpOjF6bRg/rr9hCMM7HdXN0mcb7LfTEPWOBIQfLDX RsLVz13eQ9XcTpDBSC1dbZ1/wnp6mIOI6ueT7wtNw9eALH3L6GzVQsj6jYxwUp4fU+2y b/Iz474n68GLZDQdoXdC8EuBlrLtqN8ZdAWbvRKpdHsLOsLI00HaI1TE5hIoTzxXEBRl WIjjduMCs7iYlLx3JNC0Sg9N8Elxxf3umztqoem/aMWH92Rj+XzvEqSLbgIHw7+XUViR OJBQ== 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=6gl9Lo83ig+3r4SImbYtQt6vySMRjFSrOz26uq39p6I=; b=qawZjvWA36YfMc9LHTqRi/5beg5VzVUHpJu4c+Vlb4Au5QSl/P3xaGWwLlpl/W1PmU PL/3DbXy0Kx8SqGe+LyfrbqxaO+6tAf2Osp2r/Vlc10hJNK5isvA+SgLXfvR+BLRog5D e7h22esTR6bzIdcjUz3NjdtMyKLjVkLE6xqOX3dHL9mCUTrPP3lelP0wEo0doFkhTSgs IC8xcCNbBRDzmgMgdB/0fB/Hz6dXMoAtQV47ZgYWiVo98NPhzZMl7htunbciApwn0MDn lmzqgisIRj3DJ+NWUz15cCoHJZ7R6O2h4hl9cJK5CTIoj91PNCxX+xVtuzr3hupHz2fj Iwyg== X-Gm-Message-State: AOAM5318bFaY/GCTwdtwx4Lmu0ZjUs7dUtxwjNUT+BrfeQ9HOs+ZUHXY 3eIuD77xEuMcX874tV18FjBl8/B0jf1/71U/WyceHg== X-Google-Smtp-Source: ABdhPJzjqO+/Q77KhJ+T53fnfmaPnOhExjZ+VnYdF+kYd4PXk7zk75RGHIrYUEdFHNnQQZXXCI5Y1dX1d5fX3tWilv0= X-Received: by 2002:a05:6512:200a:: with SMTP id a10mr7450509lfb.358.1613572786280; Wed, 17 Feb 2021 06:39:46 -0800 (PST) MIME-Version: 1.0 References: <20210217110907.85120-1-songmuchun@bytedance.com> In-Reply-To: <20210217110907.85120-1-songmuchun@bytedance.com> From: Shakeel Butt Date: Wed, 17 Feb 2021 06:39:34 -0800 Message-ID: Subject: Re: [PATCH v2] mm: memcontrol: fix swap undercounting in cgroup2 To: Muchun Song Cc: Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , Cgroups , Linux MM , LKML , Michal Hocko , stable@vger.kernel.org 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 Wed, Feb 17, 2021 at 3:09 AM Muchun Song wrote: > > When pages are swapped in, the VM may retain the swap copy to avoid > repeated writes in the future. It's also retained if shared pages are > faulted back in some processes, but not in others. During that time we > have an in-memory copy of the page, as well as an on-swap copy. Cgroup1 > and cgroup2 handle these overlapping lifetimes slightly differently > due to the nature of how they account memory and swap: > > Cgroup1 has a unified memory+swap counter that tracks a data page > regardless whether it's in-core or swapped out. On swapin, we transfer > the charge from the swap entry to the newly allocated swapcache page, > even though the swap entry might stick around for a while. That's why > we have a mem_cgroup_uncharge_swap() call inside mem_cgroup_charge(). > > Cgroup2 tracks memory and swap as separate, independent resources and > thus has split memory and swap counters. On swapin, we charge the > newly allocated swapcache page as memory, while the swap slot in turn > must remain charged to the swap counter as long as its allocated too. > > The cgroup2 logic was broken by commit 2d1c498072de ("mm: memcontrol: > make swap tracking an integral part of memory control"), because it > accidentally removed the do_memsw_account() check in the branch inside > mem_cgroup_uncharge() that was supposed to tell the difference between > the charge transfer in cgroup1 and the separate counters in cgroup2. > > As a result, cgroup2 currently undercounts retained swap to varying > degrees: swap slots are cached up to 50% of the configured limit or > total available swap space; partially faulted back shared pages are > only limited by physical capacity. This in turn allows cgroups to > significantly overconsume their alloted swap space. > > Add the do_memsw_account() check back to fix this problem. > > Fixes: 2d1c498072de ("mm: memcontrol: make swap tracking an integral part of memory control") > Signed-off-by: Muchun Song > Acked-by: Johannes Weiner > Reviewed-by: Shakeel Butt > Acked-by: Michal Hocko > Cc: stable@vger.kernel.org # 5.8+ > --- > v2: > - update commit log and add a comment to the code. Very thanks to Johannes. > > mm/memcontrol.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index ed5cc78a8dbf..2efbb4f71d5f 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -6771,7 +6771,19 @@ int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask) > memcg_check_events(memcg, page); > local_irq_enable(); > > - if (PageSwapCache(page)) { > + /* > + * Cgroup1's unified memory+swap counter has been charged with the > + * new swapcache page, finish the transfer by uncharging the swap > + * slot. The swap slot would also get uncharged when it dies, but > + * it can stick around indefinitely and we'd count the page twice > + * the entire time. > + * > + * Cgroup2 has separate resource counters for memory and swap, > + * so this is a non-issue here. Memory and swap charge lifetimes > + * correspond 1:1 to page and swap slot lifetimes: we charge the > + * page to memory here, and uncharge swap when the slot is freed. > + */ > + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && PageSwapCache(page)) { do_memsw_account() instead of !cgroup_subsys_on_dfl(memory_cgrp_subsys). > swp_entry_t entry = { .val = page_private(page) }; > /* > * The swap entry might not get freed for a long time, > -- > 2.11.0 >