[PATCH 18/28] mm, page_alloc: Shorten the page allocator fast path

[Mel Gorman]

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 <mgor...@techsingularity.net>
---
 mm/page_alloc.c | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 835a1c434832..7a5f6ff4ea06 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3392,22 +3392,17 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int 
order,
 
        /* 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);
 
        /*
         * When updating a task's mems_allowed, it is possible to race with
@@ -3420,6 +3415,12 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int 
order,
                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);
-- 
2.6.4