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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_RED 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 4C7A6C433E9 for ; Mon, 28 Dec 2020 11:34:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1512222583 for ; Mon, 28 Dec 2020 11:34:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727035AbgL1LeP (ORCPT ); Mon, 28 Dec 2020 06:34:15 -0500 Received: from mail.kernel.org ([198.145.29.99]:57918 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727266AbgL1LeL (ORCPT ); Mon, 28 Dec 2020 06:34:11 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2169E229C6; Mon, 28 Dec 2020 11:33:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1609155210; bh=mYhMQSWtJDDv0Iib83f7Tl4ZL9v/d0xJ9BXaMzJonB4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=wdqij7gzDR+Ukvmesk4qBlF3VzoCfv1ijXUc76tjPzwdjOs2o8v2QBoJEXX02cyxw t+mMSIGcBWF6RgZUaBEQiZgVJ4uEu//aCoZVkV7sS3VuhXB99KmpnYreHG5SFUDxRS JcS91okyLBpURcuxMJy0gvXjBQoI9lPVuWDEXF+8= Date: Mon, 28 Dec 2020 12:31:23 +0100 From: Greg KH To: Shaoying Xu Cc: stable@vger.kernel.org, fllinden@amazon.com, samjonas@amazon.com, surajjs@amazon.com Subject: Re: [PATCH 4.14] mm: memcontrol: fix excessive complexity in memory.stat reporting Message-ID: References: <20201221193531.GA10070@amazon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201221193531.GA10070@amazon.com> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Dec 21, 2020 at 07:35:31PM +0000, Shaoying Xu wrote: > From: Johannes Weiner > > [ Upstream commit a983b5ebee57209c99f68c8327072f25e0e6e3da ] > > We've seen memory.stat reads in top-level cgroups take up to fourteen > seconds during a userspace bug that created tens of thousands of ghost > cgroups pinned by lingering page cache. > > Even with a more reasonable number of cgroups, aggregating memory.stat > is unnecessarily heavy. The complexity is this: > > nr_cgroups * nr_stat_items * nr_possible_cpus > > where the stat items are ~70 at this point. With 128 cgroups and 128 > CPUs - decent, not enormous setups - reading the top-level memory.stat > has to aggregate over a million per-cpu counters. This doesn't scale. > > Instead of spreading the source of truth across all CPUs, use the > per-cpu counters merely to batch updates to shared atomic counters. > > This is the same as the per-cpu stocks we use for charging memory to the > shared atomic page_counters, and also the way the global vmstat counters > are implemented. > > Vmstat has elaborate spilling thresholds that depend on the number of > CPUs, amount of memory, and memory pressure - carefully balancing the > cost of counter updates with the amount of per-cpu error. That's > because the vmstat counters are system-wide, but also used for decisions > inside the kernel (e.g. NR_FREE_PAGES in the allocator). Neither is > true for the memory controller. > > Use the same static batch size we already use for page_counter updates > during charging. The per-cpu error in the stats will be 128k, which is > an acceptable ratio of cores to memory accounting granularity. > > [hannes@cmpxchg.org: fix warning in __this_cpu_xchg() calls] > Link: http://lkml.kernel.org/r/20171201135750.GB8097@cmpxchg.org > Link: http://lkml.kernel.org/r/20171103153336.24044-3-hannes@cmpxchg.org > Signed-off-by: Johannes Weiner > Acked-by: Vladimir Davydov > Cc: Michal Hocko > Signed-off-by: Andrew Morton > Signed-off-by: Linus Torvalds > Cc: stable@vger.kernel.org c9019e9: mm: memcontrol: eliminate raw access to stat and event counters > Cc: stable@vger.kernel.org 2845426: mm: memcontrol: implement lruvec stat functions on top of each other > Cc: stable@vger.kernel.org > [shaoyi@amazon.com: resolved the conflict brought by commit 17ffa29c355658c8e9b19f56cbf0388500ca7905 in mm/memcontrol.c by contextual fix] > Signed-off-by: Shaoying Xu > --- > The excessive complexity in memory.stat reporting was fixed in v4.16 but didn't appear to make it to 4.14 stable. When backporting this patch, there is a small conflict brought by commit 17ffa29c355658c8e9b19f56cbf0388500ca7905 within free_mem_cgroup_per_node_info() of mm/memcontrol.c and can be resolved by contextual fix. > > include/linux/memcontrol.h | 96 +++++++++++++++++++++++++++--------------- > mm/memcontrol.c | 101 +++++++++++++++++++++++---------------------- > 2 files changed, 113 insertions(+), 84 deletions(-) This patch does not apply to the 4.14.y tree, please fix it up and resend it if you wish to see it applied there. thanks, greg k-h