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=-15.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 C91AAC4332D for ; Thu, 4 Feb 2021 10:25:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9AEA06024A for ; Thu, 4 Feb 2021 10:25:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235412AbhBDKYj (ORCPT ); Thu, 4 Feb 2021 05:24:39 -0500 Received: from relay.sw.ru ([185.231.240.75]:60854 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235342AbhBDKYe (ORCPT ); Thu, 4 Feb 2021 05:24:34 -0500 Received: from [192.168.15.247] by relay.sw.ru with esmtp (Exim 4.94) (envelope-from ) id 1l7bn1-001fia-Ri; Thu, 04 Feb 2021 13:23:07 +0300 Subject: Re: [v6 PATCH 11/11] mm: vmscan: shrink deferred objects proportional to priority To: Yang Shi , guro@fb.com, vbabka@suse.cz, shakeelb@google.com, david@fromorbit.com, hannes@cmpxchg.org, mhocko@suse.com, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210203172042.800474-1-shy828301@gmail.com> <20210203172042.800474-12-shy828301@gmail.com> From: Kirill Tkhai Message-ID: <8c11f94a-bd1a-3311-2160-0f2c83994a53@virtuozzo.com> Date: Thu, 4 Feb 2021 13:23:08 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210203172042.800474-12-shy828301@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03.02.2021 20:20, Yang Shi wrote: > The number of deferred objects might get windup to an absurd number, and it > results in clamp of slab objects. It is undesirable for sustaining workingset. > > So shrink deferred objects proportional to priority and cap nr_deferred to twice > of cache items. > > The idea is borrowed fron Dave Chinner's patch: > https://lore.kernel.org/linux-xfs/20191031234618.15403-13-david@fromorbit.com/ > > Tested with kernel build and vfs metadata heavy workload in our production > environment, no regression is spotted so far. > > Signed-off-by: Yang Shi For some time I was away from this do_shrink_slab() magic formulas and recent changes, so I hope somebody else, who is being in touch with this, can review. > --- > mm/vmscan.c | 40 +++++----------------------------------- > 1 file changed, 5 insertions(+), 35 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 574d920c4cab..d0a86170854b 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -649,7 +649,6 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, > */ > nr = count_nr_deferred(shrinker, shrinkctl); > > - total_scan = nr; > if (shrinker->seeks) { > delta = freeable >> priority; > delta *= 4; > @@ -663,37 +662,9 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, > delta = freeable / 2; > } > > + total_scan = nr >> priority; > total_scan += delta; > - if (total_scan < 0) { > - pr_err("shrink_slab: %pS negative objects to delete nr=%ld\n", > - shrinker->scan_objects, total_scan); > - total_scan = freeable; > - next_deferred = nr; > - } else > - next_deferred = total_scan; > - > - /* > - * We need to avoid excessive windup on filesystem shrinkers > - * due to large numbers of GFP_NOFS allocations causing the > - * shrinkers to return -1 all the time. This results in a large > - * nr being built up so when a shrink that can do some work > - * comes along it empties the entire cache due to nr >>> > - * freeable. This is bad for sustaining a working set in > - * memory. > - * > - * Hence only allow the shrinker to scan the entire cache when > - * a large delta change is calculated directly. > - */ > - if (delta < freeable / 4) > - total_scan = min(total_scan, freeable / 2); > - > - /* > - * Avoid risking looping forever due to too large nr value: > - * never try to free more than twice the estimate number of > - * freeable entries. > - */ > - if (total_scan > freeable * 2) > - total_scan = freeable * 2; > + total_scan = min(total_scan, (2 * freeable)); > > trace_mm_shrink_slab_start(shrinker, shrinkctl, nr, > freeable, delta, total_scan, priority); > @@ -732,10 +703,9 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, > cond_resched(); > } > > - if (next_deferred >= scanned) > - next_deferred -= scanned; > - else > - next_deferred = 0; > + next_deferred = max_t(long, (nr - scanned), 0) + total_scan; > + next_deferred = min(next_deferred, (2 * freeable)); > + > /* > * move the unused scan count back into the shrinker in a > * manner that handles concurrent updates. Thanks