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=-16.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 E93C4C433ED for ; Thu, 8 Apr 2021 14:32:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AFB24610C7 for ; Thu, 8 Apr 2021 14:32:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231718AbhDHOcL (ORCPT ); Thu, 8 Apr 2021 10:32:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52798 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231665AbhDHOcJ (ORCPT ); Thu, 8 Apr 2021 10:32:09 -0400 Received: from mail-qk1-x72d.google.com (mail-qk1-x72d.google.com [IPv6:2607:f8b0:4864:20::72d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0135FC061761 for ; Thu, 8 Apr 2021 07:31:58 -0700 (PDT) Received: by mail-qk1-x72d.google.com with SMTP id v70so2344276qkb.8 for ; Thu, 08 Apr 2021 07:31:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=btC50RWZIR531OhYeaaK7FrT2NEPi0tjXTwyDrbtV5o=; b=i6e9rr/E1F5vh2gsAqs1AjButTuV2db5PXnLnGsrylcSpVrAPBMDWw7TlkxlPuEcfR 69vzlUrbGFl3mdMfMTrED2E20o/836zklqnPuO8grp+mwVmWtAl9sMJVQGN2R4Dfib4q Osvj9Hy/tqt2ZffewcVDUwMkxVb1ZeXE1xfdOe+xF3NssK0biDNoBBJm2sBSeWzjxNij nr9QqJj/dqmY/PhUHIQC7nJV/X2Y7+GSQPCA2WhHya1WL9wC13mjR7Cy40Od+40yG4kd Csi505C9RBKkqCoYQSty2edESBk7g/mzSEKx6/oZPMUVrtNTtAaw7umqVm4t7n/HereL hQBg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=btC50RWZIR531OhYeaaK7FrT2NEPi0tjXTwyDrbtV5o=; b=ZNmbaCfEvbkKb08zLNxR9Yghfa9qqAji4VSDsTc1JblvFelx6iCFtbRYPhVADkvkhr PmJh71d+GfSD+pcjAHwAxEyqyxhidf3PYSDD/cUQ6+e5tRNDowVidrx4+jjwuM6Esa3B cuObMfSUqVh1vMlpV/isSDsiUMKlVrhmP8BipgWFNp5AW6mSybdTXpyC3hh50bAWQ8Rc 61K2FEkyuBYf+bPfUNWf1bNJVH2QFmfOdoPQZsHTi086RdTq+sAi3JlfCkOFPpE1YVVx xfPnchZZT36HP3SlDlJwzt8tuKVzqqMknaD8VfnIniQyTdLGPUD6yNMmIsaFa6mledpF QQmA== X-Gm-Message-State: AOAM533LsHhr8gwrVFEbPT46LX4g8dIzLB+aav/yhkxeRC1n0xym9fG7 GzEQ2LTgPt1BrVQJ9+zzhJX5Zg== X-Google-Smtp-Source: ABdhPJw9myrgIvMrLTa+QlhcKS2FfWUGYkStVWOHWX2cPsEm/RDXMQIRxqvmwPYAYvSc9C/Cz2AHcg== X-Received: by 2002:a37:9d53:: with SMTP id g80mr8891089qke.499.1617892317152; Thu, 08 Apr 2021 07:31:57 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::1:cfb7]) by smtp.gmail.com with ESMTPSA id o26sm17463212qko.83.2021.04.08.07.31.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Apr 2021 07:31:56 -0700 (PDT) From: Johannes Weiner To: Andrew Morton Cc: Michal Hocko , Hugh Dickins , Shakeel Butt , Roman Gushchin , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: [PATCH] mm: page_counter: mitigate consequences of a page_counter underflow Date: Thu, 8 Apr 2021 10:31:55 -0400 Message-Id: <20210408143155.2679744-1-hannes@cmpxchg.org> X-Mailer: git-send-email 2.31.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When the unsigned page_counter underflows, even just by a few pages, a cgroup will not be able to run anything afterwards and trigger the OOM killer in a loop. Underflows shouldn't happen, but when they do in practice, we may just be off by a small amount that doesn't interfere with the normal operation - consequences don't need to be that dire. Reset the page_counter to 0 upon underflow. We'll issue a warning that the accounting will be off and then try to keep limping along. [ We used to do this with the original res_counter, where it was a more straight-forward correction inside the spinlock section. I didn't carry it forward into the lockless page counters for simplicity, but it turns out this is quite useful in practice. ] Signed-off-by: Johannes Weiner --- mm/page_counter.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mm/page_counter.c b/mm/page_counter.c index c6860f51b6c6..7d83641eb86b 100644 --- a/mm/page_counter.c +++ b/mm/page_counter.c @@ -52,9 +52,13 @@ void page_counter_cancel(struct page_counter *counter, unsigned long nr_pages) long new; new = atomic_long_sub_return(nr_pages, &counter->usage); - propagate_protected_usage(counter, new); /* More uncharges than charges? */ - WARN_ON_ONCE(new < 0); + if (WARN_ONCE(new < 0, "page_counter underflow: %ld nr_pages=%lu\n", + new, nr_pages)) { + new = 0; + atomic_long_set(&counter->usage, new); + } + propagate_protected_usage(counter, new); } /** -- 2.31.1 From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Weiner Subject: [PATCH] mm: page_counter: mitigate consequences of a page_counter underflow Date: Thu, 8 Apr 2021 10:31:55 -0400 Message-ID: <20210408143155.2679744-1-hannes@cmpxchg.org> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=btC50RWZIR531OhYeaaK7FrT2NEPi0tjXTwyDrbtV5o=; b=i6e9rr/E1F5vh2gsAqs1AjButTuV2db5PXnLnGsrylcSpVrAPBMDWw7TlkxlPuEcfR 69vzlUrbGFl3mdMfMTrED2E20o/836zklqnPuO8grp+mwVmWtAl9sMJVQGN2R4Dfib4q Osvj9Hy/tqt2ZffewcVDUwMkxVb1ZeXE1xfdOe+xF3NssK0biDNoBBJm2sBSeWzjxNij nr9QqJj/dqmY/PhUHIQC7nJV/X2Y7+GSQPCA2WhHya1WL9wC13mjR7Cy40Od+40yG4kd Csi505C9RBKkqCoYQSty2edESBk7g/mzSEKx6/oZPMUVrtNTtAaw7umqVm4t7n/HereL hQBg== List-ID: Content-Type: text/plain; charset="us-ascii" To: Andrew Morton Cc: Michal Hocko , Hugh Dickins , Shakeel Butt , Roman Gushchin , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kernel-team-b10kYP2dOMg@public.gmane.org When the unsigned page_counter underflows, even just by a few pages, a cgroup will not be able to run anything afterwards and trigger the OOM killer in a loop. Underflows shouldn't happen, but when they do in practice, we may just be off by a small amount that doesn't interfere with the normal operation - consequences don't need to be that dire. Reset the page_counter to 0 upon underflow. We'll issue a warning that the accounting will be off and then try to keep limping along. [ We used to do this with the original res_counter, where it was a more straight-forward correction inside the spinlock section. I didn't carry it forward into the lockless page counters for simplicity, but it turns out this is quite useful in practice. ] Signed-off-by: Johannes Weiner --- mm/page_counter.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mm/page_counter.c b/mm/page_counter.c index c6860f51b6c6..7d83641eb86b 100644 --- a/mm/page_counter.c +++ b/mm/page_counter.c @@ -52,9 +52,13 @@ void page_counter_cancel(struct page_counter *counter, unsigned long nr_pages) long new; new = atomic_long_sub_return(nr_pages, &counter->usage); - propagate_protected_usage(counter, new); /* More uncharges than charges? */ - WARN_ON_ONCE(new < 0); + if (WARN_ONCE(new < 0, "page_counter underflow: %ld nr_pages=%lu\n", + new, nr_pages)) { + new = 0; + atomic_long_set(&counter->usage, new); + } + propagate_protected_usage(counter, new); } /** -- 2.31.1