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

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Date:   Mon, 22 Mar 2021 09:46:27 +0800
From:   Shu Ming <sming56@...il.com>
To:     Xunlei Pang <xlpang@...ux.alibaba.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>, 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

More precisely, ss will count partial objects like denty objects with
"/sys/kernel/slab/dentry/partial"   whose number can become huge.

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.