slob: fix free block merging at head of subpage

We weren't merging freed blocks at the beginning of the free list.  Fixing
this showed a 2.5% efficiency improvement in a userspace test harness.

Signed-off-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/mm/slob.c b/mm/slob.c
index 773a7aa80ab..c56c5e57c19 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -398,6 +398,10 @@ static void slob_free(void *block, int size)
         sp->units += units;
 
         if (b < sp->free) {
+                if (b + units == sp->free) {
+                        units += slob_units(sp->free);
+                        sp->free = slob_next(sp->free);
+                }
                 set_slob(b, units, sp->free);
                 sp->free = b;
         } else {