Contiguous memory allocation can be stalled due to waiting on page writeback and/or page lock which causes unpredictable delay. It's a unavoidable cost for the requestor to get *big* contiguous memory but it's expensive for *small* contiguous memory(e.g., order-4) because caller could retry the request in different range where would have easy migratable pages without stalling.
This patch introduce __GFP_NORETRY as compaction gfp_mask in alloc_contig_range so it will fail fast without blocking when it encounters pages needed waiting.
Signed-off-by: Minchan Kim minchan@kernel.org --- mm/page_alloc.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index b031a5ae0bd5..1cdc3ee0b22e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -8491,12 +8491,16 @@ static int __alloc_contig_migrate_range(struct compact_control *cc, unsigned int nr_reclaimed; unsigned long pfn = start; unsigned int tries = 0; + unsigned int max_tries = 5; int ret = 0; struct migration_target_control mtc = { .nid = zone_to_nid(cc->zone), .gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL, };
+ if (cc->alloc_contig && cc->mode == MIGRATE_ASYNC) + max_tries = 1; + migrate_prep();
while (pfn < end || !list_empty(&cc->migratepages)) { @@ -8513,7 +8517,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc, break; } tries = 0; - } else if (++tries == 5) { + } else if (++tries == max_tries) { ret = ret < 0 ? ret : -EBUSY; break; } @@ -8564,7 +8568,7 @@ int alloc_contig_range(unsigned long start, unsigned long end, .nr_migratepages = 0, .order = -1, .zone = page_zone(pfn_to_page(start)), - .mode = MIGRATE_SYNC, + .mode = gfp_mask & __GFP_NORETRY ? MIGRATE_ASYNC : MIGRATE_SYNC, .ignore_skip_hint = true, .no_set_skip_hint = true, .gfp_mask = current_gfp_context(gfp_mask),