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authorVlastimil Babka <vbabka@suse.cz>2015-09-09 01:02:49 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2015-09-09 01:35:28 +0300
commit9fcd6d2e052eef525e94a9ae58dbe7ed4df4f5a7 (patch)
tree73352bbd22c199a0dcbd7a1a06f3bd5f5a4111ad
parent29c0dde830f8c08ceacf2d3edf6dc8ddd9a9c3c4 (diff)
downloadlinux-9fcd6d2e052eef525e94a9ae58dbe7ed4df4f5a7.tar.xz
mm, compaction: skip compound pages by order in free scanner
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>
-rw-r--r--mm/compaction.c25
1 files changed, 25 insertions, 0 deletions
diff --git a/mm/compaction.c b/mm/compaction.c
index 1ccb015ab1eb..8f64d3533990 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -437,6 +437,24 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
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;
@@ -496,6 +514,13 @@ isolate_fail:
}
+ /*
+ * 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;
+
trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
nr_scanned, total_isolated);