mm, page_alloc: shorten the page allocator fast path

The page allocator fast path checks page multiple times unnecessarily.
This patch avoids all the slowpath checks if the first allocation
attempt succeeds.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: 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/mm/page_alloc.c b/mm/page_alloc.c
index a3b7eb8..8380011 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3398,31 +3398,26 @@ retry_cpuset:
                                ac.nodemask, &ac.preferred_zone);
        if (!ac.preferred_zone) {
                page = NULL;
-               goto out;
+               goto no_zone;
        }
 
        ac.classzone_idx = zonelist_zone_idx(preferred_zoneref);
 
        /* First allocation attempt */
        page = get_page_from_freelist(alloc_mask, order, alloc_flags, &ac);
-       if (unlikely(!page)) {
-               /*
-                * Runtime PM, block IO and its error handling path
-                * can deadlock because I/O on the device might not
-                * complete.
-                */
-               alloc_mask = memalloc_noio_flags(gfp_mask);
-               ac.spread_dirty_pages = false;
-
-               page = __alloc_pages_slowpath(alloc_mask, order, &ac);
-       }
+       if (likely(page))
+               goto out;
 
-       if (kmemcheck_enabled && page)
-               kmemcheck_pagealloc_alloc(page, order, gfp_mask);
+       /*
+        * Runtime PM, block IO and its error handling path can deadlock
+        * because I/O on the device might not complete.
+        */
+       alloc_mask = memalloc_noio_flags(gfp_mask);
+       ac.spread_dirty_pages = false;
 
-       trace_mm_page_alloc(page, order, alloc_mask, ac.migratetype);
+       page = __alloc_pages_slowpath(alloc_mask, order, &ac);
 
-out:
+no_zone:
        /*
         * When updating a task's mems_allowed, it is possible to race with
         * parallel threads in such a way that an allocation can fail while
@@ -3434,6 +3429,12 @@ out:
                goto retry_cpuset;
        }
 
+out:
+       if (kmemcheck_enabled && page)
+               kmemcheck_pagealloc_alloc(page, order, gfp_mask);
+
+       trace_mm_page_alloc(page, order, alloc_mask, ac.migratetype);
+
        return page;
 }
 EXPORT_SYMBOL(__alloc_pages_nodemask);