mm, compaction: skip compound pages by order in free scanner
[ Upstream commit 683854270f84daa09baffe2b21d64ec88c614fa9 ]
[ Upstream commit 9fcd6d2e052eef525e94a9ae58dbe7ed4df4f5a7 ]
The compaction free scanner is looking for PageBuddy() pages and
skipping all others. For large compound pages such as THP or hugetlbfs,
we can save a lot of iterations if we skip them at once using their
compound_order(). This is generally unsafe and we can read a bogus
value of order due to a race, but if we are careful, the only danger is
skipping too much.
When tested with stress-highalloc from mmtests on 4GB system with 1GB
hugetlbfs pages, the vmstat compact_free_scanned count decreased by at
least 15%.
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
diff --git a/mm/compaction.c b/mm/compaction.c
index 8d010df..347e998 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -371,6 +371,24 @@
if (!valid_page)
valid_page = page;
+
+ /*
+ * For compound pages such as THP and hugetlbfs, we can save
+ * potentially a lot of iterations if we skip them at once.
+ * The check is racy, but we can consider only valid values
+ * and the only danger is skipping too much.
+ */
+ if (PageCompound(page)) {
+ unsigned int comp_order = compound_order(page);
+
+ if (likely(comp_order < MAX_ORDER)) {
+ blockpfn += (1UL << comp_order) - 1;
+ cursor += (1UL << comp_order) - 1;
+ }
+
+ goto isolate_fail;
+ }
+
if (!PageBuddy(page))
goto isolate_fail;
@@ -423,6 +441,13 @@
}
+ /*
+ * There is a tiny chance that we have read bogus compound_order(),
+ * so be careful to not go outside of the pageblock.
+ */
+ if (unlikely(blockpfn > end_pfn))
+ blockpfn = end_pfn;
+
/* Record how far we have got within the block */
*start_pfn = blockpfn;