On Mon, Feb 03, 2014 at 02:49:32AM -0800, David Rientjes wrote: > On Mon, 3 Feb 2014, Mel Gorman wrote: > > > > Page migration will fail for memory that is pinned in memory with, for > > > example, get_user_pages(). In this case, it is unnecessary to take > > > zone->lru_lock or isolating the page and passing it to page migration > > > which will ultimately fail. > > > > > > This is a racy check, the page can still change from under us, but in > > > that case we'll just fail later when attempting to move the page. > > > > > > This avoids very expensive memory compaction when faulting transparent > > > hugepages after pinning a lot of memory with a Mellanox driver. > > > > > > On a 128GB machine and pinning ~120GB of memory, before this patch we > > > see the enormous disparity in the number of page migration failures > > > because of the pinning (from /proc/vmstat): > > > > > > compact_blocks_moved 7609 > > > compact_pages_moved 3431 > > > compact_pagemigrate_failed 133219 > > > compact_stall 13 > > > > > > After the patch, it is much more efficient: > > > > > > compact_blocks_moved 7998 > > > compact_pages_moved 6403 > > > compact_pagemigrate_failed 3 > > > compact_stall 15 > > > > > > Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx> > > > --- > > > mm/compaction.c | 8 ++++++++ > > > 1 file changed, 8 insertions(+) > > > > > > diff --git a/mm/compaction.c b/mm/compaction.c > > > --- a/mm/compaction.c > > > +++ b/mm/compaction.c > > > @@ -578,6 +578,14 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc, > > > continue; > > > } > > > > > > + /* > > > + * Migration will fail if an anonymous page is pinned in memory, > > > + * so avoid taking zone->lru_lock and isolating it unnecessarily > > > + * in an admittedly racy check. > > > + */ > > > + if (!page_mapping(page) && page_count(page)) > > > + continue; > > > + Hello, I think that you need more code to skip this type of page correctly. Without page_mapped() check, this code makes migratable pages be skipped, since if page_mapped() case, page_count() may be more than zero. So I think that you need following change. (!page_mapping(page) && !page_mapped(page) && page_count(page)) 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>