• Vlastimil Babka's avatar
    mm/compaction: do not count migratepages when unnecessary · f8c9301f
    Vlastimil Babka authored
    
    
    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: default avatarVlastimil Babka <vbabka@suse.cz>
    Reviewed-by: default avatarNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
    Acked-by: default avatarMichal Nazarewicz <mina86@mina86.com>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Rik van Riel <riel@redhat.com>
    Acked-by: default avatarDavid Rientjes <rientjes@google.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    f8c9301f
compaction.h 2.88 KB