linux-kernel - [PATCH] mm: make pcp decay work with onhz

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Message-Id: <1729231600-19607-1-git-send-email-mengensun@tencent.com>
Date: Fri, 18 Oct 2024 14:06:40 +0800
From: MengEn Sun <mengensun88@...il.com>
To: akpm@...ux-foundation.org
Cc: alexjlzheng@...il.com,
	alexjlzheng@...cent.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	mengensun@...cent.com
Subject: [PATCH] mm: make pcp decay work with onhz

On Sat, 12 Oct 2024 15:43:28 -0700 akpm@...ux-foundation.org wrote:
> On Fri, 11 Oct 2024 18:36:10 +0800 alexjlzheng@...il.com wrote:
> 
> > Subject: [PATCH] mm: make pcp decay work with onhz
> 
> "NOHZ".
> 
> > Date: Fri, 11 Oct 2024 18:36:10 +0800
> > X-Mailer: git-send-email 2.39.3
> > 
> > From: MengEn Sun <mengensun@...cent.com>
> > 
> > when a cpu stops tick, quiet_vmstat may flush all the per cpu
> > statistics counter.
> > 
> > while, the shepherd is needed those counters to kick the
> > vmstat_work.
> > 
> > when a cpu in nohz with a lot of pcp pages, and do not do page
> > allocating and freeing. the pcp pages of the cpu may not be hold
> > for a long time
> > 
> > we make shepherd keep a eye on the pcp high_min and high_max
> 
> I can see what you're saying here, but it's hard to understand.  Please
> spend a little time clarifying the text?  And please start sentences
> with a capital letter!

Thank you for your suggestion
I will create a v2 version, and make text clarifyed

> 
> > --- a/mm/vmstat.c
> > +++ b/mm/vmstat.c
> > @@ -2024,8 +2024,13 @@ static bool need_update(int cpu)
> >  
> >  	for_each_populated_zone(zone) {
> >  		struct per_cpu_zonestat *pzstats = per_cpu_ptr(zone->per_cpu_zonestats, cpu);
> > +		struct per_cpu_pages *pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu);
> >  		struct per_cpu_nodestat *n;
> >  
> > +		/* in onhz or nohz full make pcp decay work */
> 
> "NOHZ".
> 
> > +		if (pcp->high_max > pcp->high_min)
> > +			return true;
> > +
> >  		/*
> >  		 * The fast way of checking if there are any vmstat diffs.
> >  		 */
> > --