Date:   Tue, 7 Mar 2023 14:20:26 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Qi Zheng <zhengqi.arch@bytedance.com>
Cc:     tkhai@ya.ru, hannes@cmpxchg.org, shakeelb@google.com,
        mhocko@kernel.org, roman.gushchin@linux.dev, muchun.song@linux.dev,
        david@redhat.com, shy828301@gmail.com, rppt@kernel.org,
        sultan@kerneltoast.com, dave@stgolabs.net,
        penguin-kernel@I-love.SAKURA.ne.jp, paulmck@kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 0/8] make slab shrink lockless
Message-Id: <20230307142026.31c964475fd3c9554a4f62cb@linux-foundation.org>
In-Reply-To: <20230307065605.58209-1-zhengqi.arch@bytedance.com>
References: <20230307065605.58209-1-zhengqi.arch@bytedance.com>
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On Tue,  7 Mar 2023 14:55:57 +0800 Qi Zheng <zhengqi.arch@bytedance.com> wrote:

> Hi all,
> 
> This patch series aims to make slab shrink lockless.

The v3 discussion did contain requests for some sort of measurements of
real-world workloads.  And Kirill did suggest a workload which could be
used for this measurement.

It's quite important that we have this info, please.  I mean, speeding
up real-world workloads is the entire point of the patchset and without
measurements, we don't know if the patchset achieves its primary
objective!


> 3. Reproduction and testing
> ===========================
> 
> We can reproduce the down_read_trylock() hotspot through the following script:
> 
> ```
> #!/bin/bash
> 
> DIR="/root/shrinker/memcg/mnt"
> 
> do_create()
> {
>     mkdir -p /sys/fs/cgroup/memory/test
>     mkdir -p /sys/fs/cgroup/perf_event/test
>     echo 4G > /sys/fs/cgroup/memory/test/memory.limit_in_bytes
>     for i in `seq 0 $1`;
>     do
>         mkdir -p /sys/fs/cgroup/memory/test/$i;
>         echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs;
>         echo $$ > /sys/fs/cgroup/perf_event/test/cgroup.procs;
>         mkdir -p $DIR/$i;
>     done
> }
> 
> do_mount()
> {
>     for i in `seq $1 $2`;
>     do
>         mount -t tmpfs $i $DIR/$i;
>     done
> }
> 
> do_touch()
> {
>     for i in `seq $1 $2`;
>     do
>         echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs;
>         echo $$ > /sys/fs/cgroup/perf_event/test/cgroup.procs;
>             dd if=/dev/zero of=$DIR/$i/file$i bs=1M count=1 &
>     done
> }
> 
> case "$1" in
>   touch)
>     do_touch $2 $3
>     ;;
>   test)
>       do_create 4000
>     do_mount 0 4000
>     do_touch 0 3000
>     ;;
>   *)
>     exit 1
>     ;;
> esac
> ```
> 
> Save the above script, then run test and touch commands. Then we can use the
> following perf command to view hotspots:

Well.  Simply runnimg

	time that-script

before and after and including the info in the changelog would be a start?