From: Vlastimil Babka <vbabka@xxxxxxx>
After commit "mm, reclaim: make should_continue_reclaim perform dryrun
detection", closer look at the function shows, that nr_reclaimed == 0
means the function will always return false. And since non-zero
nr_reclaimed implies non_zero nr_scanned, testing nr_scanned serves no
purpose, and so does the testing for __GFP_RETRY_MAYFAIL.
This patch thus cleans up the function to test only !nr_reclaimed upfront,
and remove the __GFP_RETRY_MAYFAIL test and nr_scanned parameter
completely. Comment is also updated, explaining that approximating "full
LRU list has been scanned" with nr_scanned == 0 didn't really work.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
Commit message reformatted to avoid line wrap.
mm/vmscan.c | 43 ++++++++++++++-----------------------------
1 file changed, 14 insertions(+), 29 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a386c5351592..227d10cd704b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2704,7 +2704,6 @@ static bool in_reclaim_compaction(struct scan_control *sc)
*/
static inline bool should_continue_reclaim(struct pglist_data *pgdat,
unsigned long nr_reclaimed,
- unsigned long nr_scanned,
struct scan_control *sc)
{
unsigned long pages_for_compaction;
@@ -2715,28 +2714,18 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
if (!in_reclaim_compaction(sc))
return false;
- /* Consider stopping depending on scan and reclaim activity */
- if (sc->gfp_mask & __GFP_RETRY_MAYFAIL) {
- /*
- * For __GFP_RETRY_MAYFAIL allocations, stop reclaiming if the
- * full LRU list has been scanned and we are still failing
- * to reclaim pages. This full LRU scan is potentially
- * expensive but a __GFP_RETRY_MAYFAIL caller really wants to succeed
- */
- if (!nr_reclaimed && !nr_scanned)
- return false;
- } else {
- /*
- * For non-__GFP_RETRY_MAYFAIL allocations which can presumably
- * fail without consequence, stop if we failed to reclaim
- * any pages from the last SWAP_CLUSTER_MAX number of
- * pages that were scanned. This will return to the
- * caller faster at the risk reclaim/compaction and
- * the resulting allocation attempt fails
- */
- if (!nr_reclaimed)
- return false;
- }
+ /*
+ * Stop if we failed to reclaim any pages from the last SWAP_CLUSTER_MAX
+ * number of pages that were scanned. This will return to the caller
+ * with the risk reclaim/compaction and the resulting allocation attempt
+ * fails. In the past we have tried harder for __GFP_RETRY_MAYFAIL
+ * allocations through requiring that the full LRU list has been scanned
+ * first, by assuming that zero delta of sc->nr_scanned means full LRU
+ * scan, but that approximation was wrong, and there were corner cases
+ * where always a non-zero amount of pages were scanned.
+ */
+ if (!nr_reclaimed)
+ return false;
/* If compaction would go ahead or the allocation would succeed, stop */
for (z = 0; z <= sc->reclaim_idx; z++) {
@@ -2763,11 +2752,7 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
if (get_nr_swap_pages() > 0)
inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
- return inactive_lru_pages > pages_for_compaction &&
- /*
- * avoid dryrun with plenty of inactive pages
- */
- nr_scanned && nr_reclaimed;
+ return inactive_lru_pages > pages_for_compaction;
}
static bool pgdat_memcg_congested(pg_data_t *pgdat, struct mem_cgroup *memcg)
@@ -2936,7 +2921,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
wait_iff_congested(BLK_RW_ASYNC, HZ/10);
} while (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
- sc->nr_scanned - nr_scanned, sc));
+ sc));
/*
* Kswapd gives up on balancing particular nodes after too
--
2.20.1
