linux-kernel - Re: [PATCH v2 0/3] mm/slub: Fix count

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Date:   Mon, 1 Mar 2021 18:31:35 +0800
From:   Shu Ming <sming56@...il.com>
To:     xlpang@...ux.alibaba.com
Cc:     Pekka Enberg <penberg@...il.com>, Vlastimil Babka <vbabka@...e.cz>,
        Christoph Lameter <cl@...ux.com>,
        Wen Yang <wenyang@...ux.alibaba.com>,
        Roman Gushchin <guro@...com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        David Rientjes <rientjes@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH v2 0/3] mm/slub: Fix count_partial() problem

Any progress on this?  The problem addressed by this patch has also
made jitters to our online apps which are quite annoying.

On Mon, Aug 24, 2020 at 6:05 PM xunlei <xlpang@...ux.alibaba.com> wrote:
>
> On 2020/8/20 下午10:02, Pekka Enberg wrote:
> > On Mon, Aug 10, 2020 at 3:18 PM Xunlei Pang <xlpang@...ux.alibaba.com> wrote:
> >>
> >> v1->v2:
> >> - Improved changelog and variable naming for PATCH 1~2.
> >> - PATCH3 adds per-cpu counter to avoid performance regression
> >>   in concurrent __slab_free().
> >>
> >> [Testing]
> >> On my 32-cpu 2-socket physical machine:
> >> Intel(R) Xeon(R) CPU E5-2650 v2 @ 2.60GHz
> >> perf stat --null --repeat 10 -- hackbench 20 thread 20000
> >>
> >> == original, no patched
> >>       19.211637055 seconds time elapsed                                          ( +-  0.57% )
> >>
> >> == patched with patch1~2
> >>  Performance counter stats for 'hackbench 20 thread 20000' (10 runs):
> >>
> >>       21.731833146 seconds time elapsed                                          ( +-  0.17% )
> >>
> >> == patched with patch1~3
> >>  Performance counter stats for 'hackbench 20 thread 20000' (10 runs):
> >>
> >>       19.112106847 seconds time elapsed                                          ( +-  0.64% )
> >>
> >>
> >> Xunlei Pang (3):
> >>   mm/slub: Introduce two counters for partial objects
> >>   mm/slub: Get rid of count_partial()
> >>   mm/slub: Use percpu partial free counter
> >>
> >>  mm/slab.h |   2 +
> >>  mm/slub.c | 124 +++++++++++++++++++++++++++++++++++++++++++-------------------
> >>  2 files changed, 89 insertions(+), 37 deletions(-)
> >
> > We probably need to wrap the counters under CONFIG_SLUB_DEBUG because
> > AFAICT all the code that uses them is also wrapped under it.
>
> /sys/kernel/slab/***/partial sysfs also uses it, I can wrap it with
> CONFIG_SLUB_DEBUG or CONFIG_SYSFS for backward compatibility.
>
> >
> > An alternative approach for this patch would be to somehow make the
> > lock in count_partial() more granular, but I don't know how feasible
> > that actually is.
> >
> > Anyway, I am OK with this approach:
> >
> > Reviewed-by: Pekka Enberg <penberg@...nel.org>
>
> Thanks!
>
> >
> > You still need to convince Christoph, though, because he had
> > objections over this approach.
>
> Christoph, what do you think, or any better suggestion to address this
> *in production* issue?
>
> >
> > - Pekka
> >