[PATCH] mm: micro optimise zone_watermark_ok

Having min be a signed quantity means gcc can't turn high latency divides
into shifts.  There happen to be two such divides for GFP_ATOMIC (ie.
networking, ie.  important) allocations, one of which depends on the other.
 Fixing this makes code smaller as a bonus.

Shame on somebody (probably me).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4f59d90..b5468de 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -900,7 +900,8 @@ int zone_watermark_ok(struct zone *z, int order, unsigned long mark,
                      int classzone_idx, int alloc_flags)
 {
        /* free_pages my go negative - that's OK */
-       long min = mark, free_pages = z->free_pages - (1 << order) + 1;
+       unsigned long min = mark;
+       long free_pages = z->free_pages - (1 << order) + 1;
        int o;
 
        if (alloc_flags & ALLOC_HIGH)