mm: don't call __page_cache_release for hugetlb

__put_compound_page() calls __page_cache_release() to do some freeing
work, but it's obviously for thps, not for hugetlb.  We don't care because
PageLRU is always cleared and page->mem_cgroup is always NULL for hugetlb.
But it's not correct and has potential risks, so let's make it
conditional.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Hugh Dickins <hughd@google.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/swap.c b/mm/swap.c
index e3a4fea..a7251a8 100644 (file)
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -31,6 +31,7 @@
 #include <linux/memcontrol.h>
 #include <linux/gfp.h>
 #include <linux/uio.h>
+#include <linux/hugetlb.h>
 
 #include "internal.h"
 
@@ -75,7 +76,14 @@ static void __put_compound_page(struct page *page)
 {
        compound_page_dtor *dtor;
 
-       __page_cache_release(page);
+       /*
+        * __page_cache_release() is supposed to be called for thp, not for
+        * hugetlb. This is because hugetlb page does never have PageLRU set
+        * (it's never listed to any LRU lists) and no memcg routines should
+        * be called for hugetlb (it has a separate hugetlb_cgroup.)
+        */
+       if (!PageHuge(page))
+               __page_cache_release(page);
        dtor = get_compound_page_dtor(page);
        (*dtor)(page);
 }