mm, page_alloc: remove fair zone allocation policy

The fair zone allocation policy interleaves allocation requests between
zones to avoid an age inversion problem whereby new pages are reclaimed
to balance a zone.  Reclaim is now node-based so this should no longer
be an issue and the fair zone allocation policy is not free.  This patch
removes it.

Link: http://lkml.kernel.org/r/1467970510-21195-30-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 2 insertions, 83 deletions

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index e19c081c794e..bd33e6f1bed0 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -110,7 +110,6 @@ struct zone_padding {
 enum zone_stat_item {
         /* First 128 byte cacheline (assuming 64 bit words) */
         NR_FREE_PAGES,
-        NR_ALLOC_BATCH,
         NR_ZONE_LRU_BASE, /* Used only for compaction and reclaim retry */
         NR_ZONE_LRU_ANON = NR_ZONE_LRU_BASE,
         NR_ZONE_LRU_FILE,
@@ -516,10 +515,6 @@ struct zone {
         atomic_long_t           vm_stat[NR_VM_ZONE_STAT_ITEMS];
 } ____cacheline_internodealigned_in_smp;
 
-enum zone_flags {
-        ZONE_FAIR_DEPLETED,             /* fair zone policy batch depleted */
-};
-
 enum pgdat_flags {
         PGDAT_CONGESTED,                /* pgdat has many dirty pages backed by
                                          * a congested BDI
diff --git a/mm/internal.h b/mm/internal.h
index 1e21b2d3838d..28932cd6a195 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -467,7 +467,6 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
 #define ALLOC_HIGH              0x20 /* __GFP_HIGH set */
 #define ALLOC_CPUSET            0x40 /* check for correct cpuset */
 #define ALLOC_CMA               0x80 /* allow allocations from CMA areas */
-#define ALLOC_FAIR              0x100 /* fair zone allocation */
 
 enum ttu_flags;
 struct tlbflush_unmap_batch;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c9d1720c58a3..1dd0f1f218db 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2587,7 +2587,6 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
                         else
                                 page = list_first_entry(list, struct page, lru);
 
-                        __dec_zone_state(zone, NR_ALLOC_BATCH);
                         list_del(&page->lru);
                         pcp->count--;
 
@@ -2613,15 +2612,10 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
                 spin_unlock(&zone->lock);
                 if (!page)
                         goto failed;
-                __mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order));
                 __mod_zone_freepage_state(zone, -(1 << order),
                                           get_pcppage_migratetype(page));
         }
 
-        if (atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]) <= 0 &&
-            !test_bit(ZONE_FAIR_DEPLETED, &zone->flags))
-                set_bit(ZONE_FAIR_DEPLETED, &zone->flags);
-
         __count_zone_vm_events(PGALLOC, zone, 1 << order);
         zone_statistics(preferred_zone, zone, gfp_flags);
         local_irq_restore(flags);
@@ -2832,40 +2826,18 @@ bool zone_watermark_ok_safe(struct zone *z, unsigned int order,
 }
 
 #ifdef CONFIG_NUMA
-static bool zone_local(struct zone *local_zone, struct zone *zone)
-{
-        return local_zone->node == zone->node;
-}
-
 static bool zone_allows_reclaim(struct zone *local_zone, struct zone *zone)
 {
         return node_distance(zone_to_nid(local_zone), zone_to_nid(zone)) <
                                 RECLAIM_DISTANCE;
 }
 #else   /* CONFIG_NUMA */
-static bool zone_local(struct zone *local_zone, struct zone *zone)
-{
-        return true;
-}
-
 static bool zone_allows_reclaim(struct zone *local_zone, struct zone *zone)
 {
         return true;
 }
 #endif  /* CONFIG_NUMA */
 
-static void reset_alloc_batches(struct zone *preferred_zone)
-{
-        struct zone *zone = preferred_zone->zone_pgdat->node_zones;
-
-        do {
-                mod_zone_page_state(zone, NR_ALLOC_BATCH,
-                        high_wmark_pages(zone) - low_wmark_pages(zone) -
-                        atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]));
-                clear_bit(ZONE_FAIR_DEPLETED, &zone->flags);
-        } while (zone++ != preferred_zone);
-}
-
 /*
  * get_page_from_freelist goes through the zonelist trying to allocate
  * a page.
@@ -2876,10 +2848,6 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 {
         struct zoneref *z = ac->preferred_zoneref;
         struct zone *zone;
-        bool fair_skipped = false;
-        bool apply_fair = (alloc_flags & ALLOC_FAIR);
-
-zonelist_scan:
         /*
          * Scan zonelist, looking for a zone with enough free.
          * See also __cpuset_node_allowed() comment in kernel/cpuset.c.
@@ -2894,23 +2862,6 @@ zonelist_scan:
                         !__cpuset_zone_allowed(zone, gfp_mask))
                                 continue;
                 /*
-                 * Distribute pages in proportion to the individual
-                 * zone size to ensure fair page aging.  The zone a
-                 * page was allocated in should have no effect on the
-                 * time the page has in memory before being reclaimed.
-                 */
-                if (apply_fair) {
-                        if (test_bit(ZONE_FAIR_DEPLETED, &zone->flags)) {
-                                fair_skipped = true;
-                                continue;
-                        }
-                        if (!zone_local(ac->preferred_zoneref->zone, zone)) {
-                                if (fair_skipped)
-                                        goto reset_fair;
-                                apply_fair = false;
-                        }
-                }
-                /*
                  * When allocating a page cache page for writing, we
                  * want to get it from a node that is within its dirty
                  * limit, such that no single node holds more than its
@@ -2981,23 +2932,6 @@ try_this_zone:
                 }
         }
 
-        /*
-         * The first pass makes sure allocations are spread fairly within the
-         * local node.  However, the local node might have free pages left
-         * after the fairness batches are exhausted, and remote zones haven't
-         * even been considered yet.  Try once more without fairness, and
-         * include remote zones now, before entering the slowpath and waking
-         * kswapd: prefer spilling to a remote zone over swapping locally.
-         */
-        if (fair_skipped) {
-reset_fair:
-                apply_fair = false;
-                fair_skipped = false;
-                reset_alloc_batches(ac->preferred_zoneref->zone);
-                z = ac->preferred_zoneref;
-                goto zonelist_scan;
-        }
-
         return NULL;
 }
 
@@ -3746,7 +3680,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
 {
         struct page *page;
         unsigned int cpuset_mems_cookie;
-        unsigned int alloc_flags = ALLOC_WMARK_LOW|ALLOC_FAIR;
+        unsigned int alloc_flags = ALLOC_WMARK_LOW;
         gfp_t alloc_mask = gfp_mask; /* The gfp_t that was actually used for allocation */
         struct alloc_context ac = {
                 .high_zoneidx = gfp_zone(gfp_mask),
@@ -5958,9 +5892,6 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat)
                 zone_seqlock_init(zone);
                 zone_pcp_init(zone);
 
-                /* For bootup, initialized properly in watermark setup */
-                mod_zone_page_state(zone, NR_ALLOC_BATCH, zone->managed_pages);
-
                 if (!size)
                         continue;
 
@@ -6808,10 +6739,6 @@ static void __setup_per_zone_wmarks(void)
                 zone->watermark[WMARK_LOW]  = min_wmark_pages(zone) + tmp;
                 zone->watermark[WMARK_HIGH] = min_wmark_pages(zone) + tmp * 2;
 
-                __mod_zone_page_state(zone, NR_ALLOC_BATCH,
-                        high_wmark_pages(zone) - low_wmark_pages(zone) -
-                        atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]));
-
                 spin_unlock_irqrestore(&zone->lock, flags);
         }
 
diff --git a/mm/vmstat.c b/mm/vmstat.c
index bc94968400d0..ab7f78995c89 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -921,7 +921,6 @@ int fragmentation_index(struct zone *zone, unsigned int order)
 const char * const vmstat_text[] = {
         /* enum zone_stat_item countes */
         "nr_free_pages",
-        "nr_alloc_batch",
         "nr_zone_anon_lru",
         "nr_zone_file_lru",
         "nr_zone_write_pending",
@@ -1632,10 +1631,9 @@ int vmstat_refresh(struct ctl_table *table, int write,
                 val = atomic_long_read(&vm_zone_stat[i]);
                 if (val < 0) {
                         switch (i) {
-                        case NR_ALLOC_BATCH:
                         case NR_PAGES_SCANNED:
                                 /*
-                                 * These are often seen to go negative in
+                                 * This is often seen to go negative in
                                  * recent kernels, but not to go permanently
                                  * negative.  Whilst it would be nicer not to
                                  * have exceptions, rooting them out would be