mm: slub: fix ALLOC_SLOWPATH stat

There used to be only one path out of __slab_alloc(), and ALLOC_SLOWPATH
got bumped in that exit path.  Now there are two, and a bunch of gotos.
ALLOC_SLOWPATH can now get set more than once during a single call to
__slab_alloc() which is pretty bogus.  Here's the sequence:

1. Enter __slab_alloc(), fall through all the way to the
   stat(s, ALLOC_SLOWPATH);
2. hit 'if (!freelist)', and bump DEACTIVATE_BYPASS, jump to
   new_slab (goto #1)
3. Hit 'if (c->partial)', bump CPU_PARTIAL_ALLOC, goto redo
   (goto #2)
4. Fall through in the same path we did before all the way to
   stat(s, ALLOC_SLOWPATH)
5. bump ALLOC_REFILL stat, then return

Doing this is obviously bogus.  It keeps us from being able to
accurately compare ALLOC_SLOWPATH vs.  ALLOC_FASTPATH.  It also means
that the total number of allocs always exceeds the total number of
frees.

This patch moves stat(s, ALLOC_SLOWPATH) to be called from the same
place that __slab_alloc() is.  This makes it much less likely that
ALLOC_SLOWPATH will get botched again in the spaghetti-code inside
__slab_alloc().

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Christoph Lameter <cl@linux.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/slub.c b/mm/slub.c
index 65a0a5c..d05a548 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2326,8 +2326,6 @@ redo:
        if (freelist)
                goto load_freelist;
 
-       stat(s, ALLOC_SLOWPATH);
-
        freelist = get_freelist(s, page);
 
        if (!freelist) {
@@ -2432,10 +2430,10 @@ redo:
 
        object = c->freelist;
        page = c->page;
-       if (unlikely(!object || !node_match(page, node)))
+       if (unlikely(!object || !node_match(page, node))) {
                object = __slab_alloc(s, gfpflags, node, addr, c);
-
-       else {
+               stat(s, ALLOC_SLOWPATH);
+       } else {
                void *next_object = get_freepointer_safe(s, object);
 
                /*