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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 80F16C433FE for ; Thu, 2 Dec 2021 17:41:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376440AbhLBRol (ORCPT ); Thu, 2 Dec 2021 12:44:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53026 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376415AbhLBRok (ORCPT ); Thu, 2 Dec 2021 12:44:40 -0500 Received: from mail-lj1-x22b.google.com (mail-lj1-x22b.google.com [IPv6:2a00:1450:4864:20::22b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 389EAC061757 for ; Thu, 2 Dec 2021 09:41:17 -0800 (PST) Received: by mail-lj1-x22b.google.com with SMTP id p8so1183727ljo.5 for ; Thu, 02 Dec 2021 09:41:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Sel9QLaZVY4N+mTLlgeCKeQqHTygfT86F1uxh//ubJk=; b=HBLmPCV+9oCwHZNYcNxG43IdBP8nmESwXT5WI7ZvozEylY0SxYxbx3yvK8hRsnW9oX WCoHepnTCI6wZD6uClG5zlGVdL7PxfteS4avkFUtE47j4XEgz3TYQFKsSSBSVcW+sLe8 TmPjrny5x9F6q2IbjeZXHzOnzz9jkjPuJkxA82whsbyBV4KhQW8cqDzgXVHqwhzz9iCE +/kGoTXMYMk/O/awyc60UzDdOMAeDrs6VEVaJyM7+JFUDco7xMUBt+7c7A51doDv2Irj sJQdPmtP7ubIW3L4+bSqS39T+DSuoGJvo3b4ZV4ZdbdScOj+bycogtO4gFABWdDW9rky xO/g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Sel9QLaZVY4N+mTLlgeCKeQqHTygfT86F1uxh//ubJk=; b=gmOGtNfb6lGJqOty9yACjbjuEqnYblgJeRMz5JiFC0QdCN7zBa9w7xThSG24H/pHDA e8TZxoXdS8XVT5+Zy1TOR5wVzQhDncvlgdiFb8rd9QHhriQmm7Cj81fN1F3nKp9uZDfB TRwrFnQNqq4jqNvWxC8FCYbVSryQODC7xVhEnfj6RkUyu4k6X6AnzvAV4Kc6WVnwUx5f Jmh0jiJJuKcB3alNVvprRxCiVRcexkB4uxHBLOycsAAaAYkI6iDUfbqAPm4Br31WGFoZ /dq8mcy887db0DiIIApeCtAJXBwXnfbvLbbf76l4IyB4ebVBJtD9n8piEnFRWFJxm7A2 fAVQ== X-Gm-Message-State: AOAM532ldu5CluWsOZETkqMp4X0oaldH2yQVRNMHow9Z3++DFR9kCGr5 M3GyNe1oFd6h7elTZtjGNKxYv4cEIy9Jmw1bZ8XRPQ== X-Google-Smtp-Source: ABdhPJxwsHniTL8HtWjxo0S47SHXwpQxqVedZCKIvQGSboEzg0cQOFPO30fWETeZK9KDiV3DDDoW9A9k9CWWDfdOAVQ= X-Received: by 2002:a05:651c:545:: with SMTP id q5mr12693560ljp.202.1638466875265; Thu, 02 Dec 2021 09:41:15 -0800 (PST) MIME-Version: 1.0 References: <20211202150614.22440-1-mgorman@techsingularity.net> <20211202165220.GZ3366@techsingularity.net> In-Reply-To: <20211202165220.GZ3366@techsingularity.net> From: Shakeel Butt Date: Thu, 2 Dec 2021 09:41:04 -0800 Message-ID: Subject: Re: [PATCH v4 1/1] mm: vmscan: Reduce throttling due to a failure to make progress To: Mel Gorman Cc: Andrew Morton , Michal Hocko , Vlastimil Babka , Alexey Avramov , Rik van Riel , Mike Galbraith , Darrick Wong , regressions@lists.linux.dev, Linux-fsdevel , Linux-MM , LKML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 2, 2021 at 8:52 AM Mel Gorman wrote: > > On Thu, Dec 02, 2021 at 08:30:51AM -0800, Shakeel Butt wrote: > > Hi Mel, > > > > On Thu, Dec 2, 2021 at 7:07 AM Mel Gorman wrote: > > > > > > Mike Galbraith, Alexey Avramov and Darrick Wong all reported similar > > > problems due to reclaim throttling for excessive lengths of time. > > > In Alexey's case, a memory hog that should go OOM quickly stalls for > > > several minutes before stalling. In Mike and Darrick's cases, a small > > > memcg environment stalled excessively even though the system had enough > > > memory overall. > > > > > > Commit 69392a403f49 ("mm/vmscan: throttle reclaim when no progress is being > > > made") introduced the problem although commit a19594ca4a8b ("mm/vmscan: > > > increase the timeout if page reclaim is not making progress") made it > > > worse. Systems at or near an OOM state that cannot be recovered must > > > reach OOM quickly and memcg should kill tasks if a memcg is near OOM. > > > > > > > Is there a reason we can't simply revert 69392a403f49 instead of adding > > more code/heuristics? Looking more into 69392a403f49, I don't think the > > code and commit message are in sync. > > > > For the memcg reclaim, instead of just removing congestion_wait or > > replacing it with schedule_timeout in mem_cgroup_force_empty(), why > > change the behavior of all memcg reclaim. Also this patch effectively > > reverts that behavior of 69392a403f49. > > > > It doesn't fully revert it but I did consider reverting it. The reason > why I preserved it because the intent originally was to throttle somewhat > when progress is not being made to avoid a premature OOM and I wanted to > preserve that charactersistic. Right now, this is the least harmful way > of doing it. If I understand correctly, the original intent of 69392a403f49 which you want to preserve is "avoid premature OOMs when reclaim is not making progress". Were there any complaints or bug reports on these premature OOMs? > > As more memcg, I removed the NOTHROTTLE because the primary reason why a > memcg might fail to make progress is excessive writeback and that should > still throttle. Completely failing to make progress in a memcg is most > likely due to a memcg-OOM. > > > For direct reclaimers under global pressure, why is page allocator a bad > > place for stalling on no progress reclaim? IMHO the callers of the > > reclaim should decide what to do if reclaim is not making progress. > > Because it's a layering violation and the caller has little direct control > over the reclaim retry logic. The page allocator has no visibility on > why reclaim failed only that it did fail. > Isn't it better that the reclaim returns why it is failing instead of littering the reclaim code with 'is this global reclaim', 'is this memcg reclaim', 'am I kswapd' which is also a layering violation. IMO this is the direction we should be going towards though not asking to do this now. Regarding this patch and 69392a403f49, I am still confused on the main motivation behind 69392a403f49 to change the behavior of 'direct reclaimers from page allocator'. thanks, Shakeel