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authorVlastimil Babka <vbabka@suse.cz>2017-05-09 01:54:49 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2017-05-09 03:15:10 +0300
commit282722b0d258ec23fc79d80165418fee83f01736 (patch)
tree01b33534bae259a2ad1ce7acf98e5b5632bb467b
parentd39773a0622c267fef3f79e3b1f0e7bdbad8a1a8 (diff)
downloadlinux-282722b0d258ec23fc79d80165418fee83f01736.tar.xz
mm, compaction: restrict async compaction to pageblocks of same migratetype
The migrate scanner in async compaction is currently limited to MIGRATE_MOVABLE pageblocks. This is a heuristic intended to reduce latency, based on the assumption that non-MOVABLE pageblocks are unlikely to contain movable pages. However, with the exception of THP's, most high-order allocations are not movable. Should the async compaction succeed, this increases the chance that the non-MOVABLE allocations will fallback to a MOVABLE pageblock, making the long-term fragmentation worse. This patch attempts to help the situation by changing async direct compaction so that the migrate scanner only scans the pageblocks of the requested migratetype. If it's a non-MOVABLE type and there are such pageblocks that do contain movable pages, chances are that the allocation can succeed within one of such pageblocks, removing the need for a fallback. If that fails, the subsequent sync attempt will ignore this restriction. In testing based on 4.9 kernel with stress-highalloc from mmtests configured for order-4 GFP_KERNEL allocations, this patch has reduced the number of unmovable allocations falling back to movable pageblocks by 30%. The number of movable allocations falling back is reduced by 12%. Link: http://lkml.kernel.org/r/20170307131545.28577-8-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.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.c11
-rw-r--r--mm/page_alloc.c20
2 files changed, 22 insertions, 9 deletions
diff --git a/mm/compaction.c b/mm/compaction.c
index 365b3c8ae943..206847d35978 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -986,10 +986,17 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
static bool suitable_migration_source(struct compact_control *cc,
struct page *page)
{
- if (cc->mode != MIGRATE_ASYNC)
+ int block_mt;
+
+ if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
return true;
- return is_migrate_movable(get_pageblock_migratetype(page));
+ block_mt = get_pageblock_migratetype(page);
+
+ if (cc->migratetype == MIGRATE_MOVABLE)
+ return is_migrate_movable(block_mt);
+ else
+ return block_mt == cc->migratetype;
}
/* Returns true if the page is within a block suitable for migration to */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d90792addeb9..e7486afa7fa7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3665,6 +3665,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
struct alloc_context *ac)
{
bool can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM;
+ const bool costly_order = order > PAGE_ALLOC_COSTLY_ORDER;
struct page *page = NULL;
unsigned int alloc_flags;
unsigned long did_some_progress;
@@ -3732,12 +3733,17 @@ retry_cpuset:
/*
* For costly allocations, try direct compaction first, as it's likely
- * that we have enough base pages and don't need to reclaim. Don't try
- * that for allocations that are allowed to ignore watermarks, as the
- * ALLOC_NO_WATERMARKS attempt didn't yet happen.
+ * that we have enough base pages and don't need to reclaim. For non-
+ * movable high-order allocations, do that as well, as compaction will
+ * try prevent permanent fragmentation by migrating from blocks of the
+ * same migratetype.
+ * Don't try this for allocations that are allowed to ignore
+ * watermarks, as the ALLOC_NO_WATERMARKS attempt didn't yet happen.
*/
- if (can_direct_reclaim && order > PAGE_ALLOC_COSTLY_ORDER &&
- !gfp_pfmemalloc_allowed(gfp_mask)) {
+ if (can_direct_reclaim &&
+ (costly_order ||
+ (order > 0 && ac->migratetype != MIGRATE_MOVABLE))
+ && !gfp_pfmemalloc_allowed(gfp_mask)) {
page = __alloc_pages_direct_compact(gfp_mask, order,
alloc_flags, ac,
INIT_COMPACT_PRIORITY,
@@ -3749,7 +3755,7 @@ retry_cpuset:
* Checks for costly allocations with __GFP_NORETRY, which
* includes THP page fault allocations
*/
- if (gfp_mask & __GFP_NORETRY) {
+ if (costly_order && (gfp_mask & __GFP_NORETRY)) {
/*
* If compaction is deferred for high-order allocations,
* it is because sync compaction recently failed. If
@@ -3830,7 +3836,7 @@ retry:
* Do not retry costly high order allocations unless they are
* __GFP_REPEAT
*/
- if (order > PAGE_ALLOC_COSTLY_ORDER && !(gfp_mask & __GFP_REPEAT))
+ if (costly_order && !(gfp_mask & __GFP_REPEAT))
goto nopage;
if (should_reclaim_retry(gfp_mask, order, ac, alloc_flags,