The patch titled
Subject: mm, compaction: restrict async compaction to pageblocks of same migratetype
has been added to the -mm tree. Its filename is
mm-compaction-restrict-async-compaction-to-pageblocks-of-same-migratetype.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-restrict-async-compaction-to-pageblocks-of-same-migratetype.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-compaction-restrict-async-compaction-to-pageblocks-of-same-migratetype.patch
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------------------------------------------------------
From: Vlastimil Babka <vbabka@xxxxxxx>
Subject: 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@xxxxxxx
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/compaction.c | 11 +++++++++--
mm/page_alloc.c | 22 ++++++++++++++--------
2 files changed, 23 insertions(+), 10 deletions(-)
diff -puN mm/compaction.c~mm-compaction-restrict-async-compaction-to-pageblocks-of-same-migratetype mm/compaction.c
--- a/mm/compaction.c~mm-compaction-restrict-async-compaction-to-pageblocks-of-same-migratetype
+++ a/mm/compaction.c
@@ -986,10 +986,17 @@ isolate_migratepages_range(struct compac
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 -puN mm/page_alloc.c~mm-compaction-restrict-async-compaction-to-pageblocks-of-same-migratetype mm/page_alloc.c
--- a/mm/page_alloc.c~mm-compaction-restrict-async-compaction-to-pageblocks-of-same-migratetype
+++ a/mm/page_alloc.c
@@ -3672,6 +3672,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, u
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;
@@ -3739,12 +3740,17 @@ 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.
- */
- if (can_direct_reclaim && order > PAGE_ALLOC_COSTLY_ORDER &&
- !gfp_pfmemalloc_allowed(gfp_mask)) {
+ * 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 &&
+ (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,
@@ -3756,7 +3762,7 @@ 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
@@ -3837,7 +3843,7 @@ 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,
_
Patches currently in -mm which might be from vbabka@xxxxxxx are
mm-compaction-reorder-fields-in-struct-compact_control.patch
mm-compaction-remove-redundant-watermark-check-in-compact_finished.patch
mm-page_alloc-split-smallest-stolen-page-in-fallback.patch
mm-page_alloc-count-movable-pages-when-stealing-from-pageblock.patch
mm-compaction-change-migrate_async_suitable-to-suitable_migration_source.patch
mm-compaction-add-migratetype-to-compact_control.patch
mm-compaction-restrict-async-compaction-to-pageblocks-of-same-migratetype.patch
mm-compaction-finish-whole-pageblock-to-reduce-fragmentation.patch
--
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