From: Hillf Danton <hdanton@xxxxxxxx> Subject: mm, reclaim: make should_continue_reclaim perform dryrun detection Patch series "address hugetlb page allocation stalls", v2. Allocation of hugetlb pages via sysctl or procfs can stall for minutes or hours. A simple example on a two node system with 8GB of memory is as follows: echo 4096 > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages echo 4096 > /proc/sys/vm/nr_hugepages Obviously, both allocation attempts will fall short of their 8GB goal. However, one or both of these commands may stall and not be interruptible. The issues were initially discussed in mail thread [1] and RFC code at [2]. This series addresses the issues causing the stalls. There are two distinct fixes, a cleanup, and an optimization. The reclaim patch by Hillf and compaction patch by Vlasitmil address corner cases in their respective areas. hugetlb page allocation could stall due to either of these issues. Vlasitmil added a cleanup patch after Hillf's modifications. The hugetlb patch by Mike is an optimization suggested during the debug and development process. [1] http://lkml.kernel.org/r/d38a095e-dc39-7e82-bb76-2c9247929f07@xxxxxxxxxx [2] http://lkml.kernel.org/r/20190724175014.9935-1-mike.kravetz@xxxxxxxxxx This patch (of 4): Address the issue of should_continue_reclaim returning true too often for __GFP_RETRY_MAYFAIL attempts when !nr_reclaimed and nr_scanned. This was observed during hugetlb page allocation causing stalls for minutes or hours. We can stop reclaiming pages if compaction reports it can make a progress. There might be side-effects for other high-order allocations that would potentially benefit from reclaiming more before compaction so that they would be faster and less likely to stall. However, the consequences of premature/over-reclaim are considered worse. We can also bail out of reclaiming pages if we know that there are not enough inactive lru pages left to satisfy the costly allocation. We can give up reclaiming pages too if we see dryrun occur, with the certainty of plenty of inactive pages. IOW with dryrun detected, we are sure we have reclaimed as many pages as we could. Link: http://lkml.kernel.org/r/20190806014744.15446-2-mike.kravetz@xxxxxxxxxx Signed-off-by: Hillf Danton <hdanton@xxxxxxxx> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Tested-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/vmscan.c | 28 +++++++++++++++------------- 1 file changed, 15 insertions(+), 13 deletions(-) --- a/mm/vmscan.c~mm-reclaim-make-should_continue_reclaim-perform-dryrun-detection +++ a/mm/vmscan.c @@ -2620,18 +2620,6 @@ static inline bool should_continue_recla return false; } - /* - * If we have not reclaimed enough pages for compaction and the - * inactive lists are large enough, continue reclaiming - */ - pages_for_compaction = compact_gap(sc->order); - inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE); - if (get_nr_swap_pages() > 0) - inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON); - if (sc->nr_reclaimed < pages_for_compaction && - inactive_lru_pages > pages_for_compaction) - return true; - /* If compaction would go ahead or the allocation would succeed, stop */ for (z = 0; z <= sc->reclaim_idx; z++) { struct zone *zone = &pgdat->node_zones[z]; @@ -2647,7 +2635,21 @@ static inline bool should_continue_recla ; } } - return true; + + /* + * If we have not reclaimed enough pages for compaction and the + * inactive lists are large enough, continue reclaiming + */ + pages_for_compaction = compact_gap(sc->order); + inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE); + 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; } static bool pgdat_memcg_congested(pg_data_t *pgdat, struct mem_cgroup *memcg) _
