Asynchronous compaction is used when promoting to huge pages. This is
all very nice but if there are a number of processes in compacting
memory, a large number of pages can be isolated. An "asynchronous"
process can stall for long periods of time as a result with a user
reporting that firefox can stall for 10s of seconds. This patch aborts
asynchronous compaction if too many pages are isolated as it's better to
fail a hugepage promotion than stall a process.
If accepted, this should also be considered for 2.6.39-stable. It should
also be considered for 2.6.38-stable but ideally [11bc82d6: mm:
compaction: Use async migration for __GFP_NO_KSWAPD and enforce no
writeback] would be applied to 2.6.38 before consideration.
Reported-and-Tested-by: Ury Stankevich <urykhy@xxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
mm/compaction.c | 32 ++++++++++++++++++++++++++------
1 files changed, 26 insertions(+), 6 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index 021a296..331a2ee 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -240,11 +240,20 @@ static bool too_many_isolated(struct zone *zone)
return isolated > (inactive + active) / 2;
}
+/* possible outcome of isolate_migratepages */
+typedef enum {
+ ISOLATE_ABORT, /* Abort compaction now */
+ ISOLATE_NONE, /* No pages isolated, continue scanning */
+ ISOLATE_SUCCESS, /* Pages isolated, migrate */
+} isolate_migrate_t;
+
/*
* Isolate all pages that can be migrated from the block pointed to by
* the migrate scanner within compact_control.
+ *
+ * Returns false if compaction should abort at this point due to congestion.
*/
-static unsigned long isolate_migratepages(struct zone *zone,
+static isolate_migrate_t isolate_migratepages(struct zone *zone,
struct compact_control *cc)
{
unsigned long low_pfn, end_pfn;
@@ -261,7 +270,7 @@ static unsigned long isolate_migratepages(struct zone *zone,
/* Do not cross the free scanner or scan within a memory hole */
if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
cc->migrate_pfn = end_pfn;
- return 0;
+ return ISOLATE_NONE;
}
/*
@@ -270,10 +279,14 @@ static unsigned long isolate_migratepages(struct zone *zone,
* delay for some time until fewer pages are isolated
*/
while (unlikely(too_many_isolated(zone))) {
+ /* async migration should just abort */
+ if (!cc->sync)
+ return ISOLATE_ABORT;
+
congestion_wait(BLK_RW_ASYNC, HZ/10);
if (fatal_signal_pending(current))
- return 0;
+ return ISOLATE_ABORT;
}
/* Time to isolate some pages for migration */
@@ -358,7 +371,7 @@ static unsigned long isolate_migratepages(struct zone *zone,
trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
- return cc->nr_migratepages;
+ return ISOLATE_SUCCESS;
}
/*
@@ -522,9 +535,15 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
unsigned long nr_migrate, nr_remaining;
int err;
- if (!isolate_migratepages(zone, cc))
+ switch (isolate_migratepages(zone, cc)) {
+ case ISOLATE_ABORT:
+ goto out;
+ case ISOLATE_NONE:
continue;
-
+ case ISOLATE_SUCCESS:
+ ;
+ }
+
nr_migrate = cc->nr_migratepages;
err = migrate_pages(&cc->migratepages, compaction_alloc,
(unsigned long)cc, false,
@@ -547,6 +566,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
}
+out:
/* Release free pages and check accounting */
cc->nr_freepages -= release_freepages(&cc->freepages);
VM_BUG_ON(cc->nr_freepages != 0);
--
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