mm, page_alloc: avoid looking up the first zone in a zonelist twice

The allocator fast path looks up the first usable zone in a zonelist and
then get_page_from_freelist does the same job in the zonelist iterator.
This patch preserves the necessary information.

                                             4.6.0-rc2                  4.6.0-rc2
                                        fastmark-v1r20             initonce-v1r20
  Min      alloc-odr0-1               364.00 (  0.00%)           359.00 (  1.37%)
  Min      alloc-odr0-2               262.00 (  0.00%)           260.00 (  0.76%)
  Min      alloc-odr0-4               214.00 (  0.00%)           214.00 (  0.00%)
  Min      alloc-odr0-8               186.00 (  0.00%)           186.00 (  0.00%)
  Min      alloc-odr0-16              173.00 (  0.00%)           173.00 (  0.00%)
  Min      alloc-odr0-32              165.00 (  0.00%)           165.00 (  0.00%)
  Min      alloc-odr0-64              161.00 (  0.00%)           162.00 ( -0.62%)
  Min      alloc-odr0-128             159.00 (  0.00%)           161.00 ( -1.26%)
  Min      alloc-odr0-256             168.00 (  0.00%)           170.00 ( -1.19%)
  Min      alloc-odr0-512             180.00 (  0.00%)           181.00 ( -0.56%)
  Min      alloc-odr0-1024            190.00 (  0.00%)           190.00 (  0.00%)
  Min      alloc-odr0-2048            196.00 (  0.00%)           196.00 (  0.00%)
  Min      alloc-odr0-4096            202.00 (  0.00%)           202.00 (  0.00%)
  Min      alloc-odr0-8192            206.00 (  0.00%)           205.00 (  0.49%)
  Min      alloc-odr0-16384           206.00 (  0.00%)           205.00 (  0.49%)

The benefit is negligible and the results are within the noise but each
cycle counts.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/buffer.c b/fs/buffer.c
index af0d9a8..754813a 100644 (file)
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -255,17 +255,17 @@ out:
  */
 static void free_more_memory(void)
 {
-       struct zone *zone;
+       struct zoneref *z;
        int nid;
 
        wakeup_flusher_threads(1024, WB_REASON_FREE_MORE_MEM);
        yield();
 
        for_each_online_node(nid) {
-               (void)first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
-                                               gfp_zone(GFP_NOFS), NULL,
-                                               &zone);
-               if (zone)
+
+               z = first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
+                                               gfp_zone(GFP_NOFS), NULL);
+               if (z->zone)
                        try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
                                                GFP_NOFS, NULL);
        }

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 327f0fa..4b28d2f 100644 (file)
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -959,13 +959,10 @@ static __always_inline struct zoneref *next_zones_zonelist(struct zoneref *z,
  */
 static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
                                        enum zone_type highest_zoneidx,
-                                       nodemask_t *nodes,
-                                       struct zone **zone)
+                                       nodemask_t *nodes)
 {
-       struct zoneref *z = next_zones_zonelist(zonelist->_zonerefs,
+       return next_zones_zonelist(zonelist->_zonerefs,
                                                        highest_zoneidx, nodes);
-       *zone = zonelist_zone(z);
-       return z;
 }
 
 /**
@@ -980,10 +977,17 @@ static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
  * within a given nodemask
  */
 #define for_each_zone_zonelist_nodemask(zone, z, zlist, highidx, nodemask) \
-       for (z = first_zones_zonelist(zlist, highidx, nodemask, &zone); \
+       for (z = first_zones_zonelist(zlist, highidx, nodemask), zone = zonelist_zone(z);       \
                zone;                                                   \
                z = next_zones_zonelist(++z, highidx, nodemask),        \
-                       zone = zonelist_zone(z))                        \
+                       zone = zonelist_zone(z))
+
+#define for_next_zone_zonelist_nodemask(zone, z, zlist, highidx, nodemask) \
+       for (zone = z->zone;    \
+               zone;                                                   \
+               z = next_zones_zonelist(++z, highidx, nodemask),        \
+                       zone = zonelist_zone(z))
+
 
 /**
  * for_each_zone_zonelist - helper macro to iterate over valid zones in a zonelist at or below a given zone index

diff --git a/mm/internal.h b/mm/internal.h
index 114593a..d1ddd71 100644 (file)
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -102,7 +102,7 @@ extern pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address);
 struct alloc_context {
        struct zonelist *zonelist;
        nodemask_t *nodemask;
-       struct zone *preferred_zone;
+       struct zoneref *preferred_zoneref;
        int classzone_idx;
        int migratetype;
        enum zone_type high_zoneidx;

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 7f80ebc..297d685 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1739,18 +1739,18 @@ unsigned int mempolicy_slab_node(void)
                return interleave_nodes(policy);
 
        case MPOL_BIND: {
+               struct zoneref *z;
+
                /*
                 * Follow bind policy behavior and start allocation at the
                 * first node.
                 */
                struct zonelist *zonelist;
-               struct zone *zone;
                enum zone_type highest_zoneidx = gfp_zone(GFP_KERNEL);
                zonelist = &NODE_DATA(node)->node_zonelists[0];
-               (void)first_zones_zonelist(zonelist, highest_zoneidx,
-                                                       &policy->v.nodes,
-                                                       &zone);
-               return zone ? zone->node : node;
+               z = first_zones_zonelist(zonelist, highest_zoneidx,
+                                                       &policy->v.nodes);
+               return z->zone ? z->zone->node : node;
        }
 
        default:
@@ -2266,7 +2266,7 @@ static void sp_free(struct sp_node *n)
 int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long addr)
 {
        struct mempolicy *pol;
-       struct zone *zone;
+       struct zoneref *z;
        int curnid = page_to_nid(page);
        unsigned long pgoff;
        int thiscpu = raw_smp_processor_id();
@@ -2298,6 +2298,7 @@ int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long
                break;
 
        case MPOL_BIND:
+
                /*
                 * allows binding to multiple nodes.
                 * use current page if in policy nodemask,
@@ -2306,11 +2307,11 @@ int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long
                 */
                if (node_isset(curnid, pol->v.nodes))
                        goto out;
-               (void)first_zones_zonelist(
+               z = first_zones_zonelist(
                                node_zonelist(numa_node_id(), GFP_HIGHUSER),
                                gfp_zone(GFP_HIGHUSER),
-                               &pol->v.nodes, &zone);
-               polnid = zone->node;
+                               &pol->v.nodes);
+               polnid = z->zone->node;
                break;
 
        default:

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 732875b..dba8cfd 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2704,7 +2704,7 @@ static struct page *
 get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
                                                const struct alloc_context *ac)
 {
-       struct zoneref *z;
+       struct zoneref *z = ac->preferred_zoneref;
        struct zone *zone;
        bool fair_skipped = false;
        bool apply_fair = (alloc_flags & ALLOC_FAIR);
@@ -2714,7 +2714,7 @@ zonelist_scan:
         * Scan zonelist, looking for a zone with enough free.
         * See also __cpuset_node_allowed() comment in kernel/cpuset.c.
         */
-       for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
+       for_next_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
                                                                ac->nodemask) {
                struct page *page;
                unsigned long mark;
@@ -2734,7 +2734,7 @@ zonelist_scan:
                                fair_skipped = true;
                                continue;
                        }
-                       if (!zone_local(ac->preferred_zone, zone)) {
+                       if (!zone_local(ac->preferred_zoneref->zone, zone)) {
                                if (fair_skipped)
                                        goto reset_fair;
                                apply_fair = false;
@@ -2780,7 +2780,7 @@ zonelist_scan:
                                goto try_this_zone;
 
                        if (zone_reclaim_mode == 0 ||
-                           !zone_allows_reclaim(ac->preferred_zone, zone))
+                           !zone_allows_reclaim(ac->preferred_zoneref->zone, zone))
                                continue;
 
                        ret = zone_reclaim(zone, gfp_mask, order);
@@ -2802,7 +2802,7 @@ zonelist_scan:
                }
 
 try_this_zone:
-               page = buffered_rmqueue(ac->preferred_zone, zone, order,
+               page = buffered_rmqueue(ac->preferred_zoneref->zone, zone, order,
                                gfp_mask, alloc_flags, ac->migratetype);
                if (page) {
                        if (prep_new_page(page, order, gfp_mask, alloc_flags))
@@ -2831,7 +2831,7 @@ try_this_zone:
 reset_fair:
                apply_fair = false;
                fair_skipped = false;
-               reset_alloc_batches(ac->preferred_zone);
+               reset_alloc_batches(ac->preferred_zoneref->zone);
                goto zonelist_scan;
        }
 
@@ -3114,7 +3114,7 @@ static void wake_all_kswapds(unsigned int order, const struct alloc_context *ac)
 
        for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
                                                ac->high_zoneidx, ac->nodemask)
-               wakeup_kswapd(zone, order, zone_idx(ac->preferred_zone));
+               wakeup_kswapd(zone, order, zonelist_zone_idx(ac->preferred_zoneref));
 }
 
 static inline unsigned int
@@ -3332,7 +3332,7 @@ retry:
        if ((did_some_progress && order <= PAGE_ALLOC_COSTLY_ORDER) ||
            ((gfp_mask & __GFP_REPEAT) && pages_reclaimed < (1 << order))) {
                /* Wait for some write requests to complete then retry */
-               wait_iff_congested(ac->preferred_zone, BLK_RW_ASYNC, HZ/50);
+               wait_iff_congested(ac->preferred_zoneref->zone, BLK_RW_ASYNC, HZ/50);
                goto retry;
        }
 
@@ -3370,7 +3370,6 @@ struct page *
 __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
                        struct zonelist *zonelist, nodemask_t *nodemask)
 {
-       struct zoneref *preferred_zoneref;
        struct page *page;
        unsigned int cpuset_mems_cookie;
        unsigned int alloc_flags = ALLOC_WMARK_LOW|ALLOC_FAIR;
@@ -3416,14 +3415,14 @@ retry_cpuset:
        ac.spread_dirty_pages = (gfp_mask & __GFP_WRITE);
 
        /* The preferred zone is used for statistics later */
-       preferred_zoneref = first_zones_zonelist(ac.zonelist, ac.high_zoneidx,
-                               ac.nodemask, &ac.preferred_zone);
-       if (!ac.preferred_zone) {
+       ac.preferred_zoneref = first_zones_zonelist(ac.zonelist,
+                                       ac.high_zoneidx, ac.nodemask);
+       if (!ac.preferred_zoneref) {
                page = NULL;
                goto no_zone;
        }
 
-       ac.classzone_idx = zonelist_zone_idx(preferred_zoneref);
+       ac.classzone_idx = zonelist_zone_idx(ac.preferred_zoneref);
 
        /* First allocation attempt */
        page = get_page_from_freelist(alloc_mask, order, alloc_flags, &ac);
@@ -4462,13 +4461,12 @@ static void build_zonelists(pg_data_t *pgdat)
  */
 int local_memory_node(int node)
 {
-       struct zone *zone;
+       struct zoneref *z;
 
-       (void)first_zones_zonelist(node_zonelist(node, GFP_KERNEL),
+       z = first_zones_zonelist(node_zonelist(node, GFP_KERNEL),
                                   gfp_zone(GFP_KERNEL),
-                                  NULL,
-                                  &zone);
-       return zone->node;
+                                  NULL);
+       return z->zone->node;
 }
 #endif