Re: [patch 1/2]compaction: check migrated page number

[Shaohua Li <shli@kernel.org>]

On Fri, Sep 07, 2012 at 05:52:43PM +0200, Andrea Arcangeli wrote:
> On Fri, Sep 07, 2012 at 12:12:12PM +0800, Shaohua Li wrote:
> > Subject: compaction: check migrated page number
> > 
> > isolate_migratepages_range() might isolate none pages, for example, when
> > zone->lru_lock is contended and compaction is async. In this case, we should
> > abort compaction, otherwise, compact_zone will run a useless loop and make
> > zone->lru_lock is even contended.
> > 
> > Signed-off-by: Shaohua Li <shli@fusionio.com>
> > ---
> >  mm/compaction.c |    5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > Index: linux/mm/compaction.c
> > ===================================================================
> > --- linux.orig/mm/compaction.c	2012-09-06 18:37:52.636413761 +0800
> > +++ linux/mm/compaction.c	2012-09-07 10:51:16.734081959 +0800
> > @@ -618,7 +618,7 @@ typedef enum {
> >  static isolate_migrate_t isolate_migratepages(struct zone *zone,
> >  					struct compact_control *cc)
> >  {
> > -	unsigned long low_pfn, end_pfn;
> > +	unsigned long low_pfn, end_pfn, old_low_pfn;
> >  
> >  	/* Do not scan outside zone boundaries */
> >  	low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
> > @@ -633,8 +633,9 @@ static isolate_migrate_t isolate_migrate
> >  	}
> >  
> >  	/* Perform the isolation */
> > +	old_low_pfn = low_pfn;
> >  	low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn);
> > -	if (!low_pfn)
> > +	if (!low_pfn || old_low_pfn == low_pfn)
> >  		return ISOLATE_ABORT;
> >  
> >  	cc->migrate_pfn = low_pfn;
> 
> Looks good to me.
> 
> This other below approach should also work:

Yep, the logic is the same. But your code looks prettier, thanks! I'll send a
formal path.

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