linux-kernel - Re: [PATCH v4 0/4] percpu: partial chunk depopulation

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Message-ID: <YIBt+qaZ4teb+WfW@google.com>
Date:   Wed, 21 Apr 2021 18:24:58 +0000
From:   Dennis Zhou <dennis@...nel.org>
To:     Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        Roman Gushchin <guro@...com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/4] percpu: partial chunk depopulation

On Mon, Apr 19, 2021 at 10:50:43PM +0000, Dennis Zhou wrote:
> Hello,
> 
> This series is a continuation of Roman's series in [1]. It aims to solve
> chunks holding onto free pages by adding a reclaim process to the percpu
> balance work item.
> 
> The main difference is that the nr_empty_pop_pages is now managed at
> time of isolation instead of intermixed. This helps with deciding which
> chunks to free instead of having to interleave returning chunks to
> active duty.
> 
> The allocation priority is as follows:
>   1) appropriate chunk slot increasing until fit
>   2) sidelined chunks
>   3) full free chunks
> 
> The last slot for to_depopulate is never used for allocations.
> 
> A big thanks to Roman for initiating the work and being available for
> iterating on these ideas.
> 
> This patchset contains the following 4 patches:
>   0001-percpu-factor-out-pcpu_check_block_hint.patch
>   0002-percpu-use-pcpu_free_slot-instead-of-pcpu_nr_slots-1.patch
>   0003-percpu-implement-partial-chunk-depopulation.patch
>   0004-percpu-use-reclaim-threshold-instead-of-running-for-.patch
> 
> 0001 and 0002 are clean ups. 0003 implement partial chunk depopulation
> initially from Roman. 0004 adds a reclaim threshold so we do not need to
> schedule for every page freed.
> 
> This series is on top of percpu$for-5.14 67c2669d69fb.
> 
> diffstats below:
> 
> Dennis Zhou (2):
>   percpu: use pcpu_free_slot instead of pcpu_nr_slots - 1
>   percpu: use reclaim threshold instead of running for every page
> 
> Roman Gushchin (2):
>   percpu: factor out pcpu_check_block_hint()
>   percpu: implement partial chunk depopulation
> 
>  mm/percpu-internal.h |   5 +
>  mm/percpu-km.c       |   5 +
>  mm/percpu-stats.c    |  20 ++--
>  mm/percpu-vm.c       |  30 ++++++
>  mm/percpu.c          | 252 ++++++++++++++++++++++++++++++++++++++-----
>  5 files changed, 278 insertions(+), 34 deletions(-)
> 
> Thanks,
> Dennis

I've applied this to for-5.14 with 1 modification to the batching
threshold, 4 pages is quite little, so make it 16.

Thanks,
Dennis