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[73.93.239.127]) by smtp.gmail.com with ESMTPSA id j1sm22260929pfr.78.2021.02.09.09.47.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Feb 2021 09:47:31 -0800 (PST) From: Yang Shi To: guro@fb.com, ktkhai@virtuozzo.com, vbabka@suse.cz, shakeelb@google.com, david@fromorbit.com, hannes@cmpxchg.org, mhocko@suse.com, akpm@linux-foundation.org Cc: shy828301@gmail.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [v7 PATCH 12/12] mm: vmscan: shrink deferred objects proportional to priority Date: Tue, 9 Feb 2021 09:46:46 -0800 Message-Id: <20210209174646.1310591-13-shy828301@gmail.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210209174646.1310591-1-shy828301@gmail.com> References: <20210209174646.1310591-1-shy828301@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 from 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 --- mm/vmscan.c | 40 +++++----------------------------------- 1 file changed, 5 insertions(+), 35 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 66163082cc6f..d670b119d6bd 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -654,7 +654,6 @@ 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; @@ -668,37 +667,9 @@ 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); @@ -737,10 +708,9 @@ 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. -- 2.26.2