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 <[email protected]> > Reviewed-by: Naoya Horiguchi <[email protected]> > Cc: Minchan Kim <[email protected]> > Cc: Mel Gorman <[email protected]> > Cc: Joonsoo Kim <[email protected]> > Cc: Bartlomiej Zolnierkiewicz <[email protected]> > Cc: Michal Nazarewicz <[email protected]> > Cc: Christoph Lameter <[email protected]> > Cc: Rik van Riel <[email protected]>
Acked-by: David Rientjes <[email protected]> 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
