linux-kernel - Re: + memory-hotplug-update-zone-pcp-at-memory-online.patch added to -mm tree

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Date:	Tue, 30 Jun 2009 08:58:28 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	"mel@....ul.ie" <mel@....ul.ie>,
	"Zhao, Yakui" <yakui.zhao@...el.com>
Subject: Re: + memory-hotplug-update-zone-pcp-at-memory-online.patch added
	to -mm tree

On Tue, Jun 30, 2009 at 06:17:52AM +0800, Christoph Lameter wrote:
> On Mon, 29 Jun 2009, akpm@...ux-foundation.org wrote:
> 
> > In my test, 128M memory is hot added, but zone's pcp batch is 0, which is
> > an obvious error.  When pages are onlined, zone pcp should be updated
> > accordingly.
> 
> Another side effect of the checks for unpopulated zones....?
Even for populated zones, the pcp should be updated as its value might not
be good as more memory is added.

> > diff -puN mm/page_alloc.c~memory-hotplug-update-zone-pcp-at-memory-online mm/page_alloc.c
> > --- a/mm/page_alloc.c~memory-hotplug-update-zone-pcp-at-memory-online
> > +++ a/mm/page_alloc.c
> > @@ -3135,6 +3135,31 @@ int zone_wait_table_init(struct zone *zo
> >  	return 0;
> >  }
> >
> > +static int __zone_pcp_update(void *data)
> > +{
> > +	struct zone *zone = data;
> > +	int cpu;
> > +	unsigned long batch = zone_batchsize(zone), flags;
> > +
> > +	for (cpu = 0; cpu < NR_CPUS; cpu++) {
> 
> foreach possible cpu?
Just follows zone_pcp_init(), do you think we should change that too?

> > +		struct per_cpu_pageset *pset;
> > +		struct per_cpu_pages *pcp;
> > +
> > +		pset = zone_pcp(zone, cpu);
> > +		pcp = &pset->pcp;
> > +
> > +		local_irq_save(flags);
> > +		free_pages_bulk(zone, pcp->count, &pcp->list, 0);
> 
> There are no pages in the pageset since the pcp batch is zero right?
It might not be zero for a populated zone, see above comments.

Thanks,
Shaohua
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