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mm, compaction: restrict async compaction to pageblocks of same migratetype

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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>
This commit is contained in:
Vlastimil Babka 2017-05-08 15:54:49 -07:00 committed by Linus Torvalds
parent d39773a062
commit 282722b0d2
2 changed files with 22 additions and 9 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

11
mm/compaction.c
View file

@ -986,10 +986,17 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
static bool suitable_migration_source(struct compact_control *cc, static bool suitable_migration_source(struct compact_control *cc,
struct page *page) struct page *page)
{ {
if (cc->mode != MIGRATE_ASYNC) int block_mt;
if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
return true; 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 */ /* Returns true if the page is within a block suitable for migration to */

20
mm/page_alloc.c
View file

@ -3665,6 +3665,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
struct alloc_context *ac) struct alloc_context *ac)
{ {
bool can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM; bool can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM;
const bool costly_order = order > PAGE_ALLOC_COSTLY_ORDER;
struct page *page = NULL; struct page *page = NULL;
unsigned int alloc_flags; unsigned int alloc_flags;
unsigned long did_some_progress; unsigned long did_some_progress;
@ -3732,12 +3733,17 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
/* /*
* For costly allocations, try direct compaction first, as it's likely * 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 we have enough base pages and don't need to reclaim. For non-
* that for allocations that are allowed to ignore watermarks, as the * movable high-order allocations, do that as well, as compaction will
* ALLOC_NO_WATERMARKS attempt didn't yet happen. * 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 && if (can_direct_reclaim &&
!gfp_pfmemalloc_allowed(gfp_mask)) { (costly_order ||
(order > 0 && ac->migratetype != MIGRATE_MOVABLE))
&& !gfp_pfmemalloc_allowed(gfp_mask)) {
page = __alloc_pages_direct_compact(gfp_mask, order, page = __alloc_pages_direct_compact(gfp_mask, order,
alloc_flags, ac, alloc_flags, ac,
INIT_COMPACT_PRIORITY, INIT_COMPACT_PRIORITY,
@ -3749,7 +3755,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
* Checks for costly allocations with __GFP_NORETRY, which * Checks for costly allocations with __GFP_NORETRY, which
* includes THP page fault allocations * 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, * If compaction is deferred for high-order allocations,
* it is because sync compaction recently failed. If * it is because sync compaction recently failed. If
@ -3830,7 +3836,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
* Do not retry costly high order allocations unless they are * Do not retry costly high order allocations unless they are
* __GFP_REPEAT * __GFP_REPEAT
*/ */
if (order > PAGE_ALLOC_COSTLY_ORDER && !(gfp_mask & __GFP_REPEAT)) if (costly_order && !(gfp_mask & __GFP_REPEAT))
goto nopage; goto nopage;
if (should_reclaim_retry(gfp_mask, order, ac, alloc_flags, if (should_reclaim_retry(gfp_mask, order, ac, alloc_flags,