On Wed, Jun 11, 2014 at 11:12:13AM +0900, Minchan Kim wrote: > On Mon, Jun 09, 2014 at 11:26:17AM +0200, Vlastimil Babka wrote: > > Unlike the migration scanner, the free scanner remembers the beginning of the > > last scanned pageblock in cc->free_pfn. It might be therefore rescanning pages > > uselessly when called several times during single compaction. This might have > > been useful when pages were returned to the buddy allocator after a failed > > migration, but this is no longer the case. > > > > This patch changes the meaning of cc->free_pfn so that if it points to a > > middle of a pageblock, that pageblock is scanned only from cc->free_pfn to the > > end. isolate_freepages_block() will record the pfn of the last page it looked > > at, which is then used to update cc->free_pfn. > > > > In the mmtests stress-highalloc benchmark, this has resulted in lowering the > > ratio between pages scanned by both scanners, from 2.5 free pages per migrate > > page, to 2.25 free pages per migrate page, without affecting success rates. > > > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > Reviewed-by: Minchan Kim <minchan@xxxxxxxxxx> > > Below is a nitpick. > > > Cc: Minchan Kim <minchan@xxxxxxxxxx> > > Cc: Mel Gorman <mgorman@xxxxxxx> > > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > > Cc: Michal Nazarewicz <mina86@xxxxxxxxxx> > > Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > > Cc: Christoph Lameter <cl@xxxxxxxxx> > > Cc: Rik van Riel <riel@xxxxxxxxxx> > > Cc: David Rientjes <rientjes@xxxxxxxxxx> > > --- > > mm/compaction.c | 33 ++++++++++++++++++++++++++++----- > > 1 file changed, 28 insertions(+), 5 deletions(-) > > > > diff --git a/mm/compaction.c b/mm/compaction.c > > index 83f72bd..58dfaaa 100644 > > --- a/mm/compaction.c > > +++ b/mm/compaction.c > > @@ -297,7 +297,7 @@ static bool suitable_migration_target(struct page *page) > > * (even though it may still end up isolating some pages). > > */ > > static unsigned long isolate_freepages_block(struct compact_control *cc, > > - unsigned long blockpfn, > > + unsigned long *start_pfn, > > unsigned long end_pfn, > > struct list_head *freelist, > > bool strict) > > @@ -306,6 +306,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, > > struct page *cursor, *valid_page = NULL; > > unsigned long flags; > > bool locked = false; > > + unsigned long blockpfn = *start_pfn; > > > > cursor = pfn_to_page(blockpfn); > > > > @@ -314,6 +315,9 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, > > int isolated, i; > > struct page *page = cursor; > > > > + /* Record how far we have got within the block */ > > + *start_pfn = blockpfn; > > + > > Couldn't we move this out of the loop for just one store? Hello, Vlastimil. Moreover, start_pfn can't be updated to end pfn with this approach. Is it okay? Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>