On Wed, 7 May 2014, Vlastimil Babka wrote: > During compaction, update_nr_listpages() has been used to count remaining > non-migrated and free pages after a call to migrage_pages(). The freepages > counting has become unneccessary, and it turns out that migratepages counting > is also unnecessary in most cases. > > The only situation when it's needed to count cc->migratepages is when > migrate_pages() returns with a negative error code. Otherwise, the non-negative > return value is the number of pages that were not migrated, which is exactly > the count of remaining pages in the cc->migratepages list. > > Furthermore, any non-zero count is only interesting for the tracepoint of > mm_compaction_migratepages events, because after that all remaining unmigrated > pages are put back and their count is set to 0. > > This patch therefore removes update_nr_listpages() completely, and changes the > tracepoint definition so that the manual counting is done only when the > tracepoint is enabled, and only when migrate_pages() returns a negative error > code. > > Furthermore, migrate_pages() and the tracepoints won't be called when there's > nothing to migrate. This potentially avoids some wasted cycles and reduces the > volume of uninteresting mm_compaction_migratepages events where "nr_migrated=0 > nr_failed=0". In the stress-highalloc mmtest, this was about 75% of the events. > The mm_compaction_isolate_migratepages event is better for determining that > nothing was isolated for migration, and this one was just duplicating the info. > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > Cc: Minchan Kim <minchan@xxxxxxxxxx> > Cc: Mel Gorman <mgorman@xxxxxxx> > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> > Cc: Michal Nazarewicz <mina86@xxxxxxxxxx> > Cc: Christoph Lameter <cl@xxxxxxxxx> > Cc: Rik van Riel <riel@xxxxxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> I like this, before our two patches update_nr_listpages() was expensive when called for each pageblock and being able to remove it is certainly a step in the right direction to make compaction as fast as possible. -- 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>