mm: vmscan: rework compaction-ready signaling in direct reclaim

Page reclaim for a higher-order page runs until compaction is ready, then
aborts and signals this situation through the return value of
shrink_zones().  This is an oddly specific signal to encode in the return
value of shrink_zones(), though, and can be quite confusing.

Introduce sc->compaction_ready and signal the compactability of the zones
out-of-band to free up the return value of shrink_zones() for actual zone
reclaimability.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Michal Hocko <mhocko@suse.cz>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 029c41ed884df1e0ac3bf606f9133f7fc908a6bb..bd7eb9e89ce1b20885877bcbfaaa1ff7dcd34621 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -65,6 +65,9 @@ struct scan_control {
        /* Number of pages freed so far during a call to shrink_zones() */
        unsigned long nr_reclaimed;
 
+       /* One of the zones is ready for compaction */
+       int compaction_ready;
+
        /* How many pages shrink_list() should reclaim */
        unsigned long nr_to_reclaim;
 
@@ -2298,15 +2301,11 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
 }
 
 /* Returns true if compaction should go ahead for a high-order request */
-static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
+static inline bool compaction_ready(struct zone *zone, int order)
 {
        unsigned long balance_gap, watermark;
        bool watermark_ok;
 
-       /* Do not consider compaction for orders reclaim is meant to satisfy */
-       if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
-               return false;
-
        /*
         * Compaction takes time to run and there are potentially other
         * callers using the pages just freed. Continue reclaiming until
@@ -2315,18 +2314,18 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
         */
        balance_gap = min(low_wmark_pages(zone), DIV_ROUND_UP(
                        zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO));
-       watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
+       watermark = high_wmark_pages(zone) + balance_gap + (2UL << order);
        watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
 
        /*
         * If compaction is deferred, reclaim up to a point where
         * compaction will have a chance of success when re-enabled
         */
-       if (compaction_deferred(zone, sc->order))
+       if (compaction_deferred(zone, order))
                return watermark_ok;
 
        /* If compaction is not ready to start, keep reclaiming */
-       if (!compaction_suitable(zone, sc->order))
+       if (!compaction_suitable(zone, order))
                return false;
 
        return watermark_ok;
@@ -2347,20 +2346,14 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
  *
  * If a zone is deemed to be full of pinned pages then just give it a light
  * scan then give up on it.
- *
- * This function returns true if a zone is being reclaimed for a costly
- * high-order allocation and compaction is ready to begin. This indicates to
- * the caller that it should consider retrying the allocation instead of
- * further reclaim.
  */
-static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
+static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 {
        struct zoneref *z;
        struct zone *zone;
        unsigned long nr_soft_reclaimed;
        unsigned long nr_soft_scanned;
        unsigned long lru_pages = 0;
-       bool aborted_reclaim = false;
        struct reclaim_state *reclaim_state = current->reclaim_state;
        gfp_t orig_mask;
        struct shrink_control shrink = {
@@ -2397,22 +2390,24 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
                        if (sc->priority != DEF_PRIORITY &&
                            !zone_reclaimable(zone))
                                continue;       /* Let kswapd poll it */
-                       if (IS_ENABLED(CONFIG_COMPACTION)) {
-                               /*
-                                * If we already have plenty of memory free for
-                                * compaction in this zone, don't free any more.
-                                * Even though compaction is invoked for any
-                                * non-zero order, only frequent costly order
-                                * reclamation is disruptive enough to become a
-                                * noticeable problem, like transparent huge
-                                * page allocations.
-                                */
-                               if ((zonelist_zone_idx(z) <= requested_highidx)
-                                   && compaction_ready(zone, sc)) {
-                                       aborted_reclaim = true;
-                                       continue;
-                               }
+
+                       /*
+                        * If we already have plenty of memory free for
+                        * compaction in this zone, don't free any more.
+                        * Even though compaction is invoked for any
+                        * non-zero order, only frequent costly order
+                        * reclamation is disruptive enough to become a
+                        * noticeable problem, like transparent huge
+                        * page allocations.
+                        */
+                       if (IS_ENABLED(CONFIG_COMPACTION) &&
+                           sc->order > PAGE_ALLOC_COSTLY_ORDER &&
+                           zonelist_zone_idx(z) <= requested_highidx &&
+                           compaction_ready(zone, sc->order)) {
+                               sc->compaction_ready = true;
+                               continue;
                        }
+
                        /*
                         * This steals pages from memory cgroups over softlimit
                         * and returns the number of reclaimed pages and
@@ -2450,8 +2445,6 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
         * promoted it to __GFP_HIGHMEM.
         */
        sc->gfp_mask = orig_mask;
-
-       return aborted_reclaim;
 }
 
 /* All zones in zonelist are unreclaimable? */
@@ -2495,7 +2488,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
 {
        unsigned long total_scanned = 0;
        unsigned long writeback_threshold;
-       bool aborted_reclaim;
 
        delayacct_freepages_start();
 
@@ -2506,12 +2498,15 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
                vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
                                sc->priority);
                sc->nr_scanned = 0;
-               aborted_reclaim = shrink_zones(zonelist, sc);
+               shrink_zones(zonelist, sc);
 
                total_scanned += sc->nr_scanned;
                if (sc->nr_reclaimed >= sc->nr_to_reclaim)
                        goto out;
 
+               if (sc->compaction_ready)
+                       goto out;
+
                /*
                 * If we're getting trouble reclaiming, start doing
                 * writepage even in laptop mode.
@@ -2532,7 +2527,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
                                                WB_REASON_TRY_TO_FREE_PAGES);
                        sc->may_writepage = 1;
                }
-       } while (--sc->priority >= 0 && !aborted_reclaim);
+       } while (--sc->priority >= 0);
 
 out:
        delayacct_freepages_end();
@@ -2541,7 +2536,7 @@ out:
                return sc->nr_reclaimed;
 
        /* Aborted reclaim to try compaction? don't OOM, then */
-       if (aborted_reclaim)
+       if (sc->compaction_ready)
                return 1;
 
        /* top priority shrink_zones still had more to do? don't OOM, then */