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=-3.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 CFD06C43331 for ; Tue, 31 Mar 2020 19:00:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A282D207FF for ; Tue, 31 Mar 2020 19:00:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chrisdown.name header.i=@chrisdown.name header.b="XlBIjLve" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728282AbgCaTAV (ORCPT ); Tue, 31 Mar 2020 15:00:21 -0400 Received: from mail-wr1-f65.google.com ([209.85.221.65]:35199 "EHLO mail-wr1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728124AbgCaTAT (ORCPT ); Tue, 31 Mar 2020 15:00:19 -0400 Received: by mail-wr1-f65.google.com with SMTP id d5so27483478wrn.2 for ; Tue, 31 Mar 2020 12:00:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chrisdown.name; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=W9IrgvrpAHB9aS+VPQ8RyBpYcd3EPPgK7vjW1jH9p/4=; b=XlBIjLveJjou8vYvEmG/DJx7mb+4KKLdTK5ypO1SHhbzlYriS/T8ZXZE3Wa5KV193/ Pt4nO+/WESvTu0W0j2wldBx99V2JUHDktLGmq1Mhw8wkFO2D0MY6EUQozw62SPqveQ1V D5ueKKEpdimT6w62FPk6JmNFP6h3CdsZSqftE= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=W9IrgvrpAHB9aS+VPQ8RyBpYcd3EPPgK7vjW1jH9p/4=; b=OQgRCBfOd8vCs5hFb86OhMTqmjGgQ3fOkcCmoNzwVb/pDn3BOJnYSlYW2211yooEv5 TYbYcR9CDEHD/iqAQCfr20xcwbyepn61MK7Q+O78wMZ9xIbCJ43U6knzZ9gY/e8eS0I5 ECGf6foTfZZ3P1hrmynCVhdBHqy0dTBhHDzu2rUAt/JfV8GTQs8Y4qo+GpIu+NgM4Twh 5i1tzYy5ffXOEuEBpnnC5UYDbW6fmcDjTfI++0HVkJSUWXjjSO2eP2mi8y2LNsAt8Rm0 gZf+JDUSRkt6worfuq4YraJpusueRLsFCIqPX0x4yp0H5tRiRNSfwcFRQqQllj3zCbhT vCNA== X-Gm-Message-State: ANhLgQ3k79/4Dl+QubSbVWZWNI5WbH/gBGN5K9BfrTZoRLOEOy3YzMND k7830QmojO7M7aOV2WHAUNs26kPHvK+qTg== X-Google-Smtp-Source: ADFU+vtetMwU3V29SeqsQ+M7amRpcn8G+/5XH6Mdx9niPX2FZYtRZ1RncB5huWjEgJ+5w7spOeGFGg== X-Received: by 2002:a5d:4146:: with SMTP id c6mr21051315wrq.181.1585681214980; Tue, 31 Mar 2020 12:00:14 -0700 (PDT) Received: from localhost ([2620:10d:c092:180::1:27bd]) by smtp.gmail.com with ESMTPSA id k9sm29062108wrd.74.2020.03.31.12.00.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2020 12:00:14 -0700 (PDT) Date: Tue, 31 Mar 2020 20:00:13 +0100 From: Chris Down To: Michal Hocko Cc: Andrew Morton , Johannes Weiner , Jakub Kicinski , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH] mm, memcg: Do not high throttle allocators based on wraparound Message-ID: <20200331190013.GC972283@chrisdown.name> References: <20200331152424.GA1019937@chrisdown.name> <20200331155752.GN30449@dhcp22.suse.cz> <20200331170410.GB972283@chrisdown.name> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="T4sUOijqQbZv57TR" Content-Disposition: inline In-Reply-To: <20200331170410.GB972283@chrisdown.name> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --T4sUOijqQbZv57TR Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline Chris Down writes: >Michal Hocko writes: >>I find this paragraph rather confusing. This is essentially an unsigned >>underflow when any of the memcg up the hierarchy is below the high >>limit, right? There doesn't really seem anything complex in such a >>hierarchy. > >The conditions to trigger the bug itself are easy, but having it >obviously visible in tests requires a moderately complex hierarchy, >since in the basic case ancestor_usage is "similar enough" to the test >leaf cgroup's usage. Here is another reason why this wasn't caught -- division usually renders the overage 0 anyway with such a large input. With the attached patch applied before this fix, you can see that usually division results in an overage of 0, so the result is the same. Here's an example where pid 213 is a cgroup in system.slice/foo.service hitting its own memory.high, and system.slice has no memory.high configuresd: [root@ktst ~]# cat /sys/kernel/debug/tracing/trace # tracer: nop # # entries-in-buffer/entries-written: 33/33 #P:4 # # _-----=> irqs-off # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / delay # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | (bash)-213 [002] .N.. 58.873988: mem_cgroup_handle_over_high: usage: 32, high: 1 (bash)-213 [002] .N.. 58.873993: mem_cgroup_handle_over_high: 1 overage before shifting (31) (bash)-213 [002] .N.. 58.873994: mem_cgroup_handle_over_high: 1 overage after shifting (32505856) (bash)-213 [002] .N.. 58.873995: mem_cgroup_handle_over_high: 1 overage after div (32505856) (bash)-213 [002] .N.. 58.873996: mem_cgroup_handle_over_high: 1 cgroup new overage (32505856) (bash)-213 [002] .N.. 58.873998: mem_cgroup_handle_over_high: usage: 18641, high: 2251799813685247 (bash)-213 [002] .N.. 58.873998: mem_cgroup_handle_over_high: 2 overage before shifting (18444492273895885010) (bash)-213 [002] .N.. 58.873999: mem_cgroup_handle_over_high: 2 overage after shifting (19547553792) (bash)-213 [002] .N.. 58.874000: mem_cgroup_handle_over_high: 2 overage after div (0) (bash)-213 [002] .N.. 58.874001: mem_cgroup_handle_over_high: 2 cgroup too low (0) (bash)-213 [002] .N.. 58.874002: mem_cgroup_handle_over_high: Used 1 from leaf to get result --T4sUOijqQbZv57TR Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="0001-temp.patch" >From df96928bc8d482d8b26c277c4ca0b075783c7aed Mon Sep 17 00:00:00 2001 From: Chris Down Date: Tue, 31 Mar 2020 19:16:23 +0100 Subject: [PATCH] temp --- mm/memcontrol.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index eecf003b0c56..c33e317c3667 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2328,11 +2328,14 @@ static unsigned long calculate_high_delay(struct mem_cgroup *memcg, { unsigned long penalty_jiffies; u64 max_overage = 0; + int i = 0, i_overage = 0; do { unsigned long usage, high; u64 overage; + i++; + usage = page_counter_read(&memcg->memory); high = READ_ONCE(memcg->high); @@ -2342,18 +2345,29 @@ static unsigned long calculate_high_delay(struct mem_cgroup *memcg, */ high = max(high, 1UL); + trace_printk("usage: %lu, high: %lu\n", usage, high); overage = usage - high; + trace_printk("%d overage before shifting (%llu)\n", i, overage); overage <<= MEMCG_DELAY_PRECISION_SHIFT; + trace_printk("%d overage after shifting (%llu)\n", i, overage); overage = div64_u64(overage, high); + trace_printk("%d overage after div (%llu)\n", i, overage); - if (overage > max_overage) + if (overage > max_overage) { + trace_printk("%d cgroup new overage (%llu)\n", i, overage); + i_overage = i; max_overage = overage; + } else { + trace_printk("%d cgroup too low (%llu)\n", i, overage); + } } while ((memcg = parent_mem_cgroup(memcg)) && !mem_cgroup_is_root(memcg)); if (!max_overage) return 0; + trace_printk("Used %d from leaf to get result\n", i_overage); + /* * We use overage compared to memory.high to calculate the number of * jiffies to sleep (penalty_jiffies). Ideally this value should be -- 2.26.0 --T4sUOijqQbZv57TR--