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 1A04AC433FF for ; Tue, 6 Aug 2019 16:27:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D90202086D for ; Tue, 6 Aug 2019 16:27:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="kPF7hmaf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387795AbfHFQ1U (ORCPT ); Tue, 6 Aug 2019 12:27:20 -0400 Received: from mail-wm1-f67.google.com ([209.85.128.67]:35961 "EHLO mail-wm1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730265AbfHFQ1U (ORCPT ); Tue, 6 Aug 2019 12:27:20 -0400 Received: by mail-wm1-f67.google.com with SMTP id g67so72990467wme.1 for ; Tue, 06 Aug 2019 09:27:18 -0700 (PDT) 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=Ks68pV+pQcpLEmyiOxXRz96t/W4aSnKi5+iAyNyk/gE=; b=kPF7hmafGtpnVgV3WJzmD140fPZ6avB9wiei7DSrdAx9HzVAwNo/YTaYwSr/+hs23M 2/QGGeppoE4nReQBnlBMru0ShdCxjI4+w6iCup4dH/BMo1y2+fDyYnZHO772HVj43dcV 75URyF088CdpW/HWe3m0arYmMvP7ap8wSOpisWI7s+rQSHKoahLZZ5rYSJ28x9GcP+F1 LfEiZR6X24HopMiCTspJO6/9yszxq5JS3Pw1Fpni0HhjelTngGgYqsdgmyv6F38Lv/6o kZbWRjPGH1GGOBu5Xfm2cV0qt/eLd6QW0GovJOTqITzpsy5+ujIWWBn4E07BNlkArQqP v02w== 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=Ks68pV+pQcpLEmyiOxXRz96t/W4aSnKi5+iAyNyk/gE=; b=djg5trgcC4etA3zIFFT8iEIotQd/ICHS8JgQzsQ6bohc2x26WGwgx9BiaZymfzdLIA QD86kpHs2XUYvqj6ZSwiNCDIkYkEQorgrvey63Dod64WbtTJQxApiYcl2oCQgzEF9qdL okgkcKU/oiYvv7hxZlx/kwIBpVW0iMknVDqfVfD5nduQ7eMt/iTZVHUmumVtU/ujxbCQ wWyp3NOr6ZVtAKXq5rGTN/dsvl7znqs4k6CTsa8yzx29nyMkFt3AgySAeXNJD2O80Emk F/vOSCf9B1uJaeb3oUSAEPnkqX1p95IF1F+TPXcxrUGDk5Sm3w14/9gvugp3Dos/ztLH 3Odw== X-Gm-Message-State: APjAAAWneaA+Pwp49s+i1U8jg4MgHw2bGmGh3Aog7EQ/YB7vq1fTBQfb Yb3QNWHCXIchsFFXqn1BzyPzRRKx+HHZueE3Tc4517gJXQU= X-Google-Smtp-Source: APXvYqxqH906LyRFrGKmI+Hu/5yd0tY4SJx3TP7vli5npqM8lWs74BhfL7iUa0EHu1RyEzfNfP//hvLYlxK55C3nLnU= X-Received: by 2002:a7b:c947:: with SMTP id i7mr5778477wml.77.1565108837080; Tue, 06 Aug 2019 09:27:17 -0700 (PDT) MIME-Version: 1.0 References: <20190805193148.GB4128@cmpxchg.org> <398f31f3-0353-da0c-fc54-643687bb4774@suse.cz> <20190806142728.GA12107@cmpxchg.org> <20190806143608.GE11812@dhcp22.suse.cz> In-Reply-To: <20190806143608.GE11812@dhcp22.suse.cz> From: Suren Baghdasaryan Date: Tue, 6 Aug 2019 09:27:05 -0700 Message-ID: Subject: Re: Let's talk about the elephant in the room - the Linux kernel's inability to gracefully handle low memory pressure To: Michal Hocko Cc: Johannes Weiner , Vlastimil Babka , "Artem S. Tashkinov" , LKML , linux-mm 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 On Tue, Aug 6, 2019 at 7:36 AM Michal Hocko wrote: > > On Tue 06-08-19 10:27:28, Johannes Weiner wrote: > > On Tue, Aug 06, 2019 at 11:36:48AM +0200, Vlastimil Babka wrote: > > > On 8/6/19 3:08 AM, Suren Baghdasaryan wrote: > > > >> @@ -1280,3 +1285,50 @@ static int __init psi_proc_init(void) > > > >> return 0; > > > >> } > > > >> module_init(psi_proc_init); > > > >> + > > > >> +#define OOM_PRESSURE_LEVEL 80 > > > >> +#define OOM_PRESSURE_PERIOD (10 * NSEC_PER_SEC) > > > > > > > > 80% of the last 10 seconds spent in full stall would definitely be a > > > > problem. If the system was already low on memory (which it probably > > > > is, or we would not be reclaiming so hard and registering such a big > > > > stall) then oom-killer would probably kill something before 8 seconds > > > > are passed. > > > > > > If oom killer can act faster, than great! On small embedded systems you probably > > > don't enable PSI anyway? We use PSI triggers with 1 sec tracking window. PSI averages are less useful on such systems because in 10 secs (which is the shortest PSI averaging window) memory conditions can change drastically. > > > > If my line of thinking is correct, then do we really > > > > benefit from such additional protection mechanism? I might be wrong > > > > here because my experience is limited to embedded systems with > > > > relatively small amounts of memory. > > > > > > Well, Artem in his original mail describes a minutes long stall. Things are > > > really different on a fast desktop/laptop with SSD. I have experienced this as > > > well, ending up performing manual OOM by alt-sysrq-f (then I put more RAM than > > > 8GB in the laptop). IMHO the default limit should be set so that the user > > > doesn't do that manual OOM (or hard reboot) before the mechanism kicks in. 10 > > > seconds should be fine. > > > > That's exactly what I have experienced in the past, and this was also > > the consistent story in the bug reports we have had. > > > > I suspect it requires a certain combination of RAM size, CPU speed, > > and IO capacity: the OOM killer kicks in when reclaim fails, which > > happens when all scanned LRU pages were locked and under IO. So IO > > needs to be slow enough, or RAM small enough, that the CPU can scan > > all LRU pages while they are temporarily unreclaimable (page lock). > > > > It may well be that on phones the RAM is small enough relative to CPU > > size. > > > > But on desktops/servers, we frequently see that there is a wider > > window of memory consumption in which reclaim efficiency doesn't drop > > low enough for the OOM killer to kick in. In the time it takes the CPU > > to scan through RAM, enough pages will have *just* finished reading > > for reclaim to free them again and continue to make "progress". > > > > We do know that the OOM killer might not kick in for at least 20-25 > > minutes while the system is entirely unresponsive. People usually > > don't wait this long before forcibly rebooting. In a managed fleet, > > ssh heartbeat tests eventually fail and force a reboot. Got it. Thanks for the explanation. > > I'm not sure 10s is the perfect value here, but I do think the kernel > > should try to get out of such a state, where interacting with the > > system is impossible, within a reasonable amount of time. > > > > It could be a little too short for non-interactive number-crunching > > systems... > > Would it be possible to have a module with tunning knobs as parameters > and hook into the PSI infrastructure? People can play with the setting > to their need, we wouldn't really have think about the user visible API > for the tuning and this could be easily adopted as an opt-in mechanism > without a risk of regressions. PSI averages stalls over 10, 60 and 300 seconds, so implementing 3 corresponding thresholds would be easy. The patch Johannes posted can be extended to support 3 thresholds instead of 1. I can take a stab at it if Johannes is busy. If we want more flexibility we could use PSI triggers with configurable tracking window but that's more complex and probably not worth it. > I would really love to see a simple threshing watchdog like the one you > have proposed earlier. It is self contained and easy to play with if the > parameters are not hardcoded. > > -- > Michal Hocko > SUSE Labs