linux-kernel - Re: [PATCH v2 linux-next] delayacct: track delays from memory compact

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Message-ID: <YbgwWir/Ymt/2gxE@balbir-desktop>
Date:   Tue, 14 Dec 2021 16:49:14 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     yong w <yongw.pur@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, mingo@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>, yang.yang29@....com.cn,
        wang.yong12@....com.cn
Subject: Re: [PATCH v2 linux-next] delayacct: track delays from memory compact

On Mon, Dec 13, 2021 at 09:56:08PM +0800, yong w wrote:
> Hello,  is this patch OK?
> 
> Thanks.
> 
> yong w <yongw.pur@...il.com> 于2021年12月8日周三 00:50写道：
> >
> > Balbir Singh <bsingharora@...il.com> 于2021年12月7日周二 13:16写道：
> > >
> > > On Sun, Dec 05, 2021 at 07:08:02PM +0800, yong w wrote:
> > > > Balbir Singh <bsingharora@...il.com> 于2021年12月5日周日 16:17写道：
> > > > >
> > > > > On Sat, Dec 04, 2021 at 04:09:55AM -0800, yongw.pur@...il.com wrote:
> > > > > > From: wangyong <wang.yong12@....com.cn>
> > > > > >
> > > > > > Delay accounting does not track the delay of memory compact.
> > > > > > When there is not enough free memory, tasks can spend
> > > > > > a amount of their time waiting for compact.
> > > > > >
> > > > > > To get the impact of tasks in direct memory compact, measure
> > > > > > the delay when allocating memory through memory compact.
> > > > > >
> > > > >
> > > > > Should we call this DIRECT_COMPACT and through documentation
> > > > > or name change imply that this won't work for kcompactd the
> > > > > kernel thread - based on my reading of the patches.
> > > > >
> > > > Using DIRECT_COMPACT is a little redundant，because the
> > > > delayacct stats of delay accounting is specific to tasks, it has
> > > > nothing to do with kcompactd, which is similar to the RECLAIM field.
> > > >
> > >
> > > What would we expect when we call delayacct -p <pidof kcompactd>
> > > to be output?
> > If the slow path of memory allocation is invoked in the kcompacd process,
> > there may be delays being recorded.
> >
> > > Don't feel to strongly, but it can be confusing that kcompactd
> > > has spent no time in compact'ing? Not that delayacct is used for
> > > kernel threads, but I am not sure if that use case exists today.
> > Yes, delayacct does not restrict the process of obtaining information，
> > but kcompactd is used for  compaction,  the compact delay of
> > kcompatd is not actually a delay.Maybe it can be added to the
> > document later to make it clearer.
> >
> > Thanks for your reply!

Please avoid top posting, when you say added later, I presume more
patches for documentation are coming. I am OK with the patch in that
case.

Reviewed-by: Balbir Singh <bsingharora@...il.com>

Balbir Singh