From: Vlastimil Babka <vbabka@xxxxxxx> Subject: mm, reclaim: cleanup should_continue_reclaim() 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. Link: http://lkml.kernel.org/r/20190806014744.15446-3-mike.kravetz@xxxxxxxxxx Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Acked-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Hillf Danton <hdanton@xxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/vmscan.c | 43 ++++++++++++++----------------------------- 1 file changed, 14 insertions(+), 29 deletions(-) --- a/mm/vmscan.c~mm-reclaim-cleanup-should_continue_reclaim +++ a/mm/vmscan.c @@ -2586,7 +2586,6 @@ static bool in_reclaim_compaction(struct */ 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; @@ -2597,28 +2596,18 @@ static inline bool should_continue_recla 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++) { @@ -2645,11 +2634,7 @@ static inline bool should_continue_recla 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) @@ -2794,7 +2779,7 @@ static bool shrink_node(pg_data_t *pgdat 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 _
