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authorJoonsoo Kim <iamjoonsoo.kim@lge.com>2015-02-12 22:59:53 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2015-02-13 02:54:10 (GMT)
commit932ff6bbbdcadd85b309ef4fd59d4d8a77329b8b (patch)
tree64a820151120a58e822a987e91aba65b1a46c2c2
parent372549c2a3778fd3df445819811c944ad54609ca (diff)
mm/compaction: stop the isolation when we isolate enough freepage
Currently, freepage isolation in one pageblock doesn't consider how many freepages we isolate. When I traced flow of compaction, compaction sometimes isolates more than 256 freepages to migrate just 32 pages. In this patch, freepage isolation is stopped at the point that we have more isolated freepage than isolated page for migration. This results in slowing down free page scanner and make compaction success rate higher. stress-highalloc test in mmtests with non movable order 7 allocation shows increase of compaction success rate. Compaction success rate (Compaction success * 100 / Compaction stalls, %) 27.13 : 31.82 pfn where both scanners meets on compaction complete (separate test due to enormous tracepoint buffer) (zone_start=4096, zone_end=1048576) 586034 : 654378 In fact, I didn't fully understand why this patch results in such good result. There was a guess that not used freepages are released to pcp list and on next compaction trial we won't isolate them again so compaction success rate would decrease. To prevent this effect, I tested with adding pcp drain code on release_freepages(), but, it has no good effect. Anyway, this patch reduces waste time to isolate unneeded freepages so seems reasonable. Vlastimil said: : I briefly tried it on top of the pivot-changing series and with order-9 : allocations it reduced free page scanned counter by almost 10%. No effect : on success rates (maybe because pivot changing already took care of the : scanners meeting problem) but the scanning reduction is good on its own. : : It also explains why e14c720efdd7 ("mm, compaction: remember position : within pageblock in free pages scanner") had less than expected : improvements. It would only actually stop within pageblock in case of : async compaction detecting contention. I guess that's also why the : infinite loop problem fixed by 1d5bfe1ffb5b affected so relatively few : people. Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Tested-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com> Cc: Mel Gorman <mgorman@suse.de> Cc: David Rientjes <rientjes@google.com> Cc: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/compaction.c17
1 files changed, 10 insertions, 7 deletions
diff --git a/mm/compaction.c b/mm/compaction.c
index 4954e19..782772d 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -490,6 +490,13 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
/* If a page was split, advance to the end of it */
if (isolated) {
+ cc->nr_freepages += isolated;
+ if (!strict &&
+ cc->nr_migratepages <= cc->nr_freepages) {
+ blockpfn += isolated;
+ break;
+ }
+
blockpfn += isolated - 1;
cursor += isolated - 1;
continue;
@@ -899,7 +906,6 @@ static void isolate_freepages(struct compact_control *cc)
unsigned long isolate_start_pfn; /* exact pfn we start at */
unsigned long block_end_pfn; /* end of current pageblock */
unsigned long low_pfn; /* lowest pfn scanner is able to scan */
- int nr_freepages = cc->nr_freepages;
struct list_head *freelist = &cc->freepages;
/*
@@ -924,11 +930,11 @@ static void isolate_freepages(struct compact_control *cc)
* pages on cc->migratepages. We stop searching if the migrate
* and free page scanners meet or enough free pages are isolated.
*/
- for (; block_start_pfn >= low_pfn && cc->nr_migratepages > nr_freepages;
+ for (; block_start_pfn >= low_pfn &&
+ cc->nr_migratepages > cc->nr_freepages;
block_end_pfn = block_start_pfn,
block_start_pfn -= pageblock_nr_pages,
isolate_start_pfn = block_start_pfn) {
- unsigned long isolated;
/*
* This can iterate a massively long zone without finding any
@@ -953,9 +959,8 @@ static void isolate_freepages(struct compact_control *cc)
continue;
/* Found a block suitable for isolating free pages from. */
- isolated = isolate_freepages_block(cc, &isolate_start_pfn,
+ isolate_freepages_block(cc, &isolate_start_pfn,
block_end_pfn, freelist, false);
- nr_freepages += isolated;
/*
* Remember where the free scanner should restart next time,
@@ -987,8 +992,6 @@ static void isolate_freepages(struct compact_control *cc)
*/
if (block_start_pfn < low_pfn)
cc->free_pfn = cc->migrate_pfn;
-
- cc->nr_freepages = nr_freepages;
}
/*

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