[PATCH v3 2/4] mm: failfast mode with __GFP_NORETRY in alloc_contig_range

Minchan Kim
2021-01-13T01:22:00Z

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 diffrent 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 waitting.

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 5b3923db9158..ff41ceb4db51 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8489,12 +8489,16 @@ 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)) {
@@ -8511,7 +8515,7 @@ 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;
}
@@ -8562,7 +8566,7 @@ 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),
--
2.30.0.284.gd98b1dd5eaa7-goog