linux-kernel - Re: [PATCH] kswapd: no need reclaim cma pages triggered by unmovable allocation

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Message-ID: <YCPcRj/e9NdQIV9S@dhcp22.suse.cz>
Date:   Wed, 10 Feb 2021 14:14:46 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     zhou xianrong <xianrong_zhou@....com>
Cc:     iamjoonsoo.kim@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        rostedt@...dmis.org, mingo@...hat.com, vbabka@...e.cz,
        rientjes@...gle.com, willy@...ux.intel.com,
        pankaj.gupta.linux@...il.com, bhe@...hat.com, ying.huang@...el.com,
        minchan@...nel.org, ruxian.feng@...nssion.com,
        kai.cheng@...nssion.com, zhao.xu@...nssion.com,
        yunfeng.lan@...nssion.com, zhouxianrong@....com,
        zhou xianrong <xianrong.zhou@...nssion.com>
Subject: Re: [PATCH] kswapd: no need reclaim cma pages triggered by unmovable
 allocation

On Wed 10-02-21 12:07:57, zhou xianrong wrote:
> 
> On 2021/2/9 下午5:23, Michal Hocko wrote:
> > On Tue 09-02-21 16:23:13, zhou wrote:
> > > From: zhou xianrong <xianrong.zhou@...nssion.com>
> > > 
> > > For purpose of better migration cma pages are allocated after
> > > failure movalbe allocations and are used normally for file pages
> > > or anonymous pages.
> > > 
> > > In reclaim path so many cma pages if configurated are reclaimed
> > > from lru lists in kswapd mainly or direct reclaim triggered by
> > > unmovable or reclaimable allocations. But these cma pages can not
> > > be used by original unmovable or reclaimable allocations. So the
> > > reclaim are unnecessary.
> > > 
> > > In a same system if the cma pages were configurated to large then
> > > more failture unmovable (vmalloc etc.) or reclaimable (slab etc.)
> > > allocations are arised and then more kswapd rounds are triggered
> > > and then more cma pages are reclaimed.
> > Could you be more specific? Do you have any numbers and an example
> > configuration when this is visible?
> It should be implicit.

Right but the scale of the problem is an important part of _any_ patch
justification.
-- 
Michal Hocko
SUSE Labs