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From:   Vlastimil Babka <vbabka@suse.cz>
Subject: SLUB: percpu partial object count is highly inaccurate, causing some
 memory wastage and maybe also worse tail latencies?
To:     Christoph Lameter <cl@linux.com>, Jann Horn <jannh@google.com>
Cc:     Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Roman Gushchin <guro@fb.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shakeel Butt <shakeelb@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Minchan Kim <minchan@kernel.org>,
        Michal Hocko <mhocko@kernel.org>
References: <CAG48ez2Qx5K1Cab-m8BdSibp6wLTip6ro4=-umR7BLsEgjEYzA@mail.gmail.com>
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Message-ID: <e4d89d4f-62d4-43e3-9dd7-2496e955b437@suse.cz>
Date:   Thu, 14 Jan 2021 10:27:40 +0100
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On 1/12/21 5:35 PM, Christoph Lameter wrote:
> On Tue, 12 Jan 2021, Jann Horn wrote:
> 
>> [This is not something I intend to work on myself. But since I
>> stumbled over this issue, I figured I should at least document/report
>> it, in case anyone is willing to pick it up.]
> 
> Well yeah all true. There is however a slabinfo tool that has an -s option
> to shrink all slabs.
> 
> 	slabinfo -s
> 
> So you could put that somewhere that executes if the system is
> idle or put it into cron or so.

Hm this would be similar to recommending a periodical echo > drop_caches
operation. We actually discourage from that (and yeah, some tools do that, and
we now report those in dmesg). I believe the kernel should respond to memory
pressure and not OOM prematurely by itself, including SLUB.