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=-8.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,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 4F3F4C433E0 for ; Thu, 4 Jun 2020 08:17:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2CDCC20738 for ; Thu, 4 Jun 2020 08:17:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="PTgQ328Y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727829AbgFDIRF (ORCPT ); Thu, 4 Jun 2020 04:17:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52180 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726912AbgFDIRF (ORCPT ); Thu, 4 Jun 2020 04:17:05 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EBC6CC05BD1E for ; Thu, 4 Jun 2020 01:17:04 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id f187so7169178ybc.2 for ; Thu, 04 Jun 2020 01:17:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=dBhjvQ74rk87+xvmHCHMByl/N/LCyKOoeijL1Gf/O4E=; b=PTgQ328YnDam3JMX89/M53yQXWYuipuKp4wnwdFku6bBvCivR7xb1c6eFbsE+H+Kf4 kUz2G12JgF+LiQiAvLcWiRPuS0BSKFkpjKDRGWJQU89Um5iJXLvZzIIvV6LxQ283D9F+ UfAsuYZVjO+4tzvsTuDLhBPoFbJSSRZDif7PNa+4qrRuQYyG41Ts9TU6opuqooH4lOEn ldJUeiGFtsgSHv/VsJ3A4ZpuG5nrBSLfJ7WXy6/KT4T1L6RxrFlTuKyHPs0hOqWc9Bql KpLW0eUirQTTztYWMtEFOJdK3aCJjOX6KyAN15F4dJAqw+nrHapuFvPs4ZDklaAw/JBl uhYw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=dBhjvQ74rk87+xvmHCHMByl/N/LCyKOoeijL1Gf/O4E=; b=eHK0VZivHfGU6KdFDat+x8MEDtMBIm/18hta67IYsJQlSSVVlDwIcxShUGCtUp1/X7 mB0/13UZ5Qek/oX8vqK0dj9HyI6h30ogtSixFa2x7x5DrnFWfeleBkbKK23RP1pgEFnS mQpr57+qHYw2B1R44a13ZQXgzIlmWdWv4GTyR3dIYYXxRQskDHsj75OZVG+TFWkZsiAZ orUYoZy2pMLPfg74mLV5pg5eablvOvpqVvMUE6q2I64NmQSIto3IzmiTJP71SKTLoTUC muQOTdFxVNi0jpfmC8i8aRGrnrQB01BT3IdQpL2eAbVh1S4HV42EU/uu1O62//n5PxnJ KQQw== X-Gm-Message-State: AOAM532jId0Ubjup7i8+aJGb7QrDiEHCifiOZIKCqdc2QWA2DmXwZo3P a/fmY5FXuIw3/k1mMY443ihRKZLqX58E X-Google-Smtp-Source: ABdhPJw8DqlSWOZDSYtk3HzYUQDUrhkIKVQXAMPIq2tKNiuSr8cBaTwCXqaZggl1HvweWqrSm1EDwrkxlI++ X-Received: by 2002:a25:cb48:: with SMTP id b69mr1168096ybg.252.1591258624144; Thu, 04 Jun 2020 01:17:04 -0700 (PDT) Date: Thu, 04 Jun 2020 01:17:01 -0700 In-Reply-To: Message-Id: Mime-Version: 1.0 References: <20200601032204.124624-1-gthelen@google.com> Subject: Re: [PATCH] shmem, memcg: enable memcg aware shrinker From: Greg Thelen To: Yang Shi Cc: Hugh Dickins , Andrew Morton , Kirill Tkhai , Linux MM , Linux Kernel Mailing List , stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Yang Shi wrote: > On Sun, May 31, 2020 at 8:22 PM Greg Thelen wrote: >> >> Since v4.19 commit b0dedc49a2da ("mm/vmscan.c: iterate only over charged >> shrinkers during memcg shrink_slab()") a memcg aware shrinker is only >> called when the per-memcg per-node shrinker_map indicates that the >> shrinker may have objects to release to the memcg and node. >> >> shmem_unused_huge_count and shmem_unused_huge_scan support the per-tmpfs >> shrinker which advertises per memcg and numa awareness. The shmem >> shrinker releases memory by splitting hugepages that extend beyond >> i_size. >> >> Shmem does not currently set bits in shrinker_map. So, starting with >> b0dedc49a2da, memcg reclaim avoids calling the shmem shrinker under >> pressure. This leads to undeserved memcg OOM kills. >> Example that reliably sees memcg OOM kill in unpatched kernel: >> FS=/tmp/fs >> CONTAINER=/cgroup/memory/tmpfs_shrinker >> mkdir -p $FS >> mount -t tmpfs -o huge=always nodev $FS >> # Create 1000 MB container, which shouldn't suffer OOM. >> mkdir $CONTAINER >> echo 1000M > $CONTAINER/memory.limit_in_bytes >> echo $BASHPID >> $CONTAINER/cgroup.procs >> # Create 4000 files. Ideally each file uses 4k data page + a little >> # metadata. Assume 8k total per-file, 32MB (4000*8k) should easily >> # fit within container's 1000 MB. But if data pages use 2MB >> # hugepages (due to aggressive huge=always) then files consume 8GB, >> # which hits memcg 1000 MB limit. >> for i in {1..4000}; do >> echo . > $FS/$i >> done > > It looks all the inodes which have tail THP beyond i_size are on one > single list, then the shrinker actually just splits the first > nr_to_scan inodes. But since the list is not memcg aware, so it seems > it may split the THPs which are not charged to the victim memcg and > the victim memcg still may suffer from pre-mature oom, right? Correct. shmem_unused_huge_shrink() is not memcg aware. In response to memcg pressure it will split the post-i_size tails of nr_to_scan tmpfs inodes regardless of if they're charged to the under-pressure memcg. do_shrink_slab() looks like it'll repeatedly call shmem_unused_huge_shrink(). So it will split tails of many inodes. So I think it'll avoid the oom by over shrinking. This is not ideal. But it seems better than undeserved oom kill. I think the solution (as Kirill Tkhai suggested) a memcg-aware index would solve both: 1) avoid premature oom by registering shrinker to responding to memcg pressure 2) avoid shrinking/splitting inodes unrelated to the under-pressure memcg I can certainly look into that (thanks Kirill for the pointers). In the short term I'm still interested in avoiding premature OOMs with the original thread (i.e. restore pre-4.19 behavior to shmem shrinker for memcg pressure). I plan to test and repost v2.