>
> The number of LRU pages, dirty pages and writeback pages must be accounted
> for on both zones and nodes because of the reclaim retry logic, compaction
> retry logic and highmem calculations all depending on per-zone stats.
>
> The retry logic is only critical for allocations that can use any zones.
> Hence this patch will not retry reclaim or compaction for such allocations.
> This should not be a problem for reclaim as zone-constrained allocations
> are immune from OOM kill. For retries, a very rough approximation is made
> whether to retry or not. While it is possible this will make the wrong
> decision on occasion, it will not infinite loop as the number of reclaim
> attempts is capped by MAX_RECLAIM_RETRIES.
>
> The highmem calculations only care about the global count of file pages
> in highmem. Hence, a global counter is used instead of per-zone stats.
> With this, the per-zone double accounting disappears.
>
> Suggested by: Michal Hocko <mhocko@xxxxxxxxxx>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> ---
Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
> include/linux/mm_inline.h | 20 +++++++++++--
> include/linux/mmzone.h | 4 ---
> include/linux/swap.h | 1 -
> mm/compaction.c | 22 ++++++++++++++-
> mm/migrate.c | 2 --
> mm/page-writeback.c | 13 ++++-----
> mm/page_alloc.c | 71 ++++++++++++++++++++++++++++++++---------------
> mm/vmscan.c | 16 -----------
> mm/vmstat.c | 3 --
> 9 files changed, 92 insertions(+), 60 deletions(-)
>
[...]
> @@ -3445,6 +3445,7 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
> {
> struct zone *zone;
> struct zoneref *z;
> + pg_data_t *current_pgdat = NULL;
>
> /*
> * Make sure we converge to OOM if we cannot make any progress
> @@ -3454,6 +3455,14 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
> return false;
>
> /*
> + * Blindly retry allocation requests that cannot use all zones. We do
> + * not have a reliable and fast means of calculating reclaimable, dirty
> + * and writeback pages in eligible zones.
> + */
> + if (IS_ENABLED(CONFIG_HIGHMEM) && !is_highmem_idx(gfp_zone(gfp_mask)))
> + goto out;
> +
> + /*
> * Keep reclaiming pages while there is a chance this will lead somewhere.
> * If none of the target zones can satisfy our allocation request even
> * if all reclaimable pages are considered then we are screwed and have
> @@ -3463,36 +3472,54 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
> ac->nodemask) {
> unsigned long available;
> unsigned long reclaimable;
> + unsigned long write_pending = 0;
> + int zid;
> +
> + if (current_pgdat == zone->zone_pgdat)
> + continue;
>
> - available = reclaimable = zone_reclaimable_pages(zone);
> + current_pgdat = zone->zone_pgdat;
> + available = reclaimable = pgdat_reclaimable_pages(current_pgdat);
> available -= DIV_ROUND_UP(no_progress_loops * available,
> MAX_RECLAIM_RETRIES);
> - available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
> + write_pending = node_page_state(current_pgdat, NR_WRITEBACK) +
> + node_page_state(current_pgdat, NR_FILE_DIRTY);
>
> - /*
> - * Would the allocation succeed if we reclaimed the whole
> - * available?
> - */
> - if (__zone_watermark_ok(zone, order, min_wmark_pages(zone),
> - ac_classzone_idx(ac), alloc_flags, available)) {
> - /*
> - * If we didn't make any progress and have a lot of
> - * dirty + writeback pages then we should wait for
> - * an IO to complete to slow down the reclaim and
> - * prevent from pre mature OOM
> - */
> - if (!did_some_progress) {
> - unsigned long write_pending;
> + /* Account for all free pages on eligible zones */
> + for (zid = 0; zid <= zone_idx(zone); zid++) {
> + struct zone *acct_zone = ¤t_pgdat->node_zones[zid];
>
> - write_pending = zone_page_state_snapshot(zone,
> - NR_ZONE_WRITE_PENDING);
> + available += zone_page_state_snapshot(acct_zone, NR_FREE_PAGES);
> + }
>
> - if (2 * write_pending > reclaimable) {
> - congestion_wait(BLK_RW_ASYNC, HZ/10);
> - return true;
> - }
> + /*
> + * If we didn't make any progress and have a lot of
> + * dirty + writeback pages then we should wait for an IO to
> + * complete to slow down the reclaim and prevent from premature
> + * OOM.
> + */
> + if (!did_some_progress) {
> + if (2 * write_pending > reclaimable) {
> + congestion_wait(BLK_RW_ASYNC, HZ/10);
> + return true;
> }
> + }
>
> + /*
> + * Would the allocation succeed if we reclaimed the whole
> + * available? This is approximate because there is no
> + * accurate count of reclaimable pages per zone.
> + */
> + for (zid = 0; zid <= zone_idx(zone); zid++) {
> + struct zone *check_zone = ¤t_pgdat->node_zones[zid];
> + unsigned long estimate;
> +
> + estimate = min(check_zone->managed_pages, available);
> + if (__zone_watermark_ok(check_zone, order,
> + min_wmark_pages(check_zone), ac_classzone_idx(ac),
> + alloc_flags, available)) {
> + }
Stray indent?
> +out:
> /*
> * Memory allocation/reclaim might be called from a WQ
> * context and the current implementation of the WQ
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 151c30dd27e2..c538a8cab43b 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
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