linux-kernel - Re: [PATCH v4 1/3] mm/slub: Introduce two counters for partial objects

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Date:   Mon, 22 Mar 2021 11:22:43 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Shu Ming <sming56@...il.com>,
        Xunlei Pang <xlpang@...ux.alibaba.com>
Cc:     Christoph Lameter <cl@...ux.com>, Christoph Lameter <cl@...two.de>,
        Pekka Enberg <penberg@...nel.org>,
        Roman Gushchin <guro@...com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        Wen Yang <wenyang@...ux.alibaba.com>,
        James Wang <jnwang@...ux.alibaba.com>
Subject: Re: [PATCH v4 1/3] mm/slub: Introduce two counters for partial
 objects

On 3/22/21 2:46 AM, Shu Ming wrote:
> More precisely, ss will count partial objects like denty objects with
> "/sys/kernel/slab/dentry/partial"   whose number can become huge.

Uh, that's interesting. Would you know what exactly it uses the value for? I can
think of several reasons why it might be misleading.

> On Thu, Mar 18, 2021 at 8:56 PM Xunlei Pang <xlpang@...ux.alibaba.com> wrote:
>>
>>
>>
>> On 3/18/21 8:18 PM, Vlastimil Babka wrote:
>> > On 3/17/21 8:54 AM, Xunlei Pang wrote:
>> >> The node list_lock in count_partial() spends long time iterating
>> >> in case of large amount of partial page lists, which can cause
>> >> thunder herd effect to the list_lock contention.
>> >>
>> >> We have HSF RT(High-speed Service Framework Response-Time) monitors,
>> >> the RT figures fluctuated randomly, then we deployed a tool detecting
>> >> "irq off" and "preempt off" to dump the culprit's calltrace, capturing
>> >> the list_lock cost nearly 100ms with irq off issued by "ss", this also
>> >> caused network timeouts.
>> >
>> > I forgot to ask, how does "ss" come into this? It displays network connections
>> > AFAIK. Does it read any SLUB counters or slabinfo?
>> >
>>
>> ss may access /proc/slabinfo to acquire network related slab statistics.
>