linux-kernel - Re: [PATCH 5/6] mm/page_alloc: Protect PCP lists with a spinlock

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Date:   Wed, 20 Apr 2022 16:35:04 +0200
From:   Nicolas Saenz Julienne <nsaenzju@...hat.com>
To:     Hillf Danton <hdanton@...a.com>,
        Mel Gorman <mgorman@...hsingularity.net>
Cc:     Marcelo Tosatti <mtosatti@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 5/6] mm/page_alloc: Protect PCP lists with a spinlock

Hi Hillf,

On Wed, 2022-04-20 at 22:02 +0800, Hillf Danton wrote:
> On Wed, 20 Apr 2022 10:59:05 +0100 Mel Gorman wrote:
> >  void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp)
> >  {
> > -	unsigned long flags;
> >  	int to_drain, batch;
> >  
> > -	local_lock_irqsave(&pagesets.lock, flags);
> >  	batch = READ_ONCE(pcp->batch);
> >  	to_drain = min(pcp->count, batch);
> > -	if (to_drain > 0)
> > +	if (to_drain > 0) {
> > +		unsigned long flags;
> > +
> > +		/* free_pcppages_bulk expects IRQs disabled for zone->lock */
> > +		local_irq_save(flags);
> > +
> > +		spin_lock(&pcp->lock);
> 
> Nit, spin_lock_irqsave() instead.

See cover letter's:

"This series is a partial series. Follow-on work would allow the local_irq_save
to be converted to a local_irq to avoid IRQs being disabled/enabled in most
cases. However, there are enough corner cases that it deserves a series on its
own separated by one kernel release and the priority right now is to avoid
interference of high priority tasks."

Regards,

-- 
Nicolás Sáenz