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 <vba...@suse.cz> > Reviewed-by: Naoya Horiguchi <n-horigu...@ah.jp.nec.com> > Cc: Minchan Kim <minc...@kernel.org> > Cc: Mel Gorman <mgor...@suse.de> > Cc: Joonsoo Kim <iamjoonsoo....@lge.com> > Cc: Bartlomiej Zolnierkiewicz <b.zolnier...@samsung.com> > Cc: Michal Nazarewicz <min...@mina86.com> > Cc: Christoph Lameter <c...@linux.com> > Cc: Rik van Riel <r...@redhat.com>
Acked-by: David Rientjes <rient...@google.com> 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
