On Tue, Jun 07, 2011 at 04:07:05PM +0100, Mel Gorman wrote:
> 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.
>
> Reported-and-tested-by: Ury Stankevich <urykhy@xxxxxxxxx>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> ---
> mm/compaction.c | 28 +++++++++++++++++++++++-----
> 1 files changed, 23 insertions(+), 5 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 5c744ab..cb28580 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -251,11 +251,18 @@ 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.
> */
> -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;
> @@ -272,7 +279,7 @@ 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;
> }
>
> /*
> @@ -281,10 +288,14 @@ 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 */
> @@ -369,7 +380,7 @@ static unsigned long isolate_migratepages(struct zone *zone,
>
> trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
>
> - return cc->nr_migratepages;
> + return ISOLATE_SUCCESS;
> }
>
> /*
> @@ -533,8 +544,14 @@ 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:
In this case, you change old behavior slightly.
In old case, we return COMPACT_PARTIAL to cancel migration.
But this patch makes to return COMPACT_SUCCESS.
At present, return value of compact_zone is only used by __alloc_pages_direct_compact
and it only consider COMPACT_SKIPPED so it would be not a problem.
But I think it would be better to return COMPACT_PARTIAL instead of COMPACT_CONTINUE
for consistency with compact_finished and right semantic for the future user of compact_zone.
--
Kind regards
Minchan Kim
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