linux-kernel - Re: [RFC PATCH 1/2] psi: introduce memory.pressure.stat

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Date:   Tue, 6 Sep 2022 11:40:51 +0000
From:   CGEL <cgel.zte@...il.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     akpm@...ux-foundation.org, tj@...nel.org, axboe@...nel.dk,
        vdavydov.dev@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, cgel <cgel@....com.cn>
Subject: Re: [RFC PATCH 1/2] psi: introduce memory.pressure.stat

On Wed, Aug 17, 2022 at 02:59:48AM +0000, CGEL wrote:
> On Wed, Aug 03, 2022 at 09:55:39AM -0400, Johannes Weiner wrote:
> > On Mon, Aug 01, 2022 at 12:42:04AM +0000, cgel.zte@...il.com wrote:
> > 
> > This doubles the psi cache footprint on every context switch, wakeup,
> > sleep, etc. in the scheduler. You're also adding more branches to
> > those same paths. It'll measurably affect everybody who is using psi.
> > 
> > Yet, in the years of using psi in production myself, I've never felt
> > the need for what this patch provides. There are event counters for
> > everything that contributes to pressure, and it's never been hard to
> > rootcause spikes. There are also things like bpftrace that let you
> > identify who is stalling for how long in order to do one-off tuning
> > and systems introspection.
> > 
> We think this patch is not for rootcause spikes, it's for automatic optimize
> memory besides oomd, especially for sysctl adjustment. For example if we see
> much pressure of direct reclaim the automatic optimize program might turn up
> watermark_scale_factor.
> The base idea is that this patch gives user a brief UI to know what kind of
> memory pressure the system is suffering, and to optimize the system in a fine
> grain. It could provide data for user to adjust watermark_boost_factor,
> extfrag_threshold, compaction_proactiveness,transparent_hugepage/defrag,
> swappiness, vfs_cache_pressure, madvise(), which may not easy for to do
> before.
> 
> It's not easy for automatic optimize program to use tools likes bpftrace or
> ftrace to do this.
> 
> While we may use CONFIG_PSI_XX or bootparam to turn on/off this patch to avoid
> additional footprint for user who not need this.

Hi
   Do you think this is praciseable?