linux-kernel - Re: [PATCH 11/12] mm, page_alloc: Reserve pageblocks for high-order atomic allocations on demand

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Date:	Wed, 26 Aug 2015 16:38:18 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/12] mm, page_alloc: Reserve pageblocks for high-order
 atomic allocations on demand

On Wed, Aug 26, 2015 at 04:53:52PM +0200, Michal Hocko wrote:
> > 
> > Overall, this is a small reduction but the reserves are small relative to the
> > number of allocation requests. In early versions of the patch, the failure
> > rate reduced by a much larger amount but that required much larger reserves
> > and perversely made atomic allocations seem more reliable than regular allocations.
> 
> Have you considered a counter for vmstat/zoneinfo so that we have an overview
> about the memory consumed for this reserve?
> 

It should already be available in /proc/pagetypeinfo

> > Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> 
> Acked-by: Michal Hocko <mhocko@...e.com>
> 
> [...]
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index d5ce050ebe4f..2415f882b89c 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> [...]
> > @@ -1645,10 +1725,16 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
> >   * Call me with the zone->lock already held.
> >   */
> >  static struct page *__rmqueue(struct zone *zone, unsigned int order,
> > -						int migratetype)
> > +				int migratetype, gfp_t gfp_flags)
> >  {
> >  	struct page *page;
> >  
> > +	if (unlikely(order && (gfp_flags & __GFP_ATOMIC))) {
> > +		page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
> > +		if (page)
> > +			goto out;
> 
> I guess you want to change migratetype to MIGRATE_HIGHATOMIC in the
> successful case so the tracepoint reports this properly.
> 

Yes, thanks.

-- 
Mel Gorman
SUSE Labs
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