[PATCH] Fix mm regression bug: nommu use compound page in slab allocator -- added one comment

[PATCH] Fix mm regression bug: nommu use compound page in slab allocator -- added one comment

[Luke Yang]

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Hi all,

 The earlier patch to consolidate mmu and nommu page allocation
and refcounting by using compound pages for nommu allocations
had a bug: kmalloc slabs who's pages were initially allocated
by a non-__GFP_COMP allocator could be passed into mm/nommu.c
kmalloc allocations which really wanted __GFP_COMP underlying
pages. Fix that by having nommu pass __GFP_COMP to all higher order
slab allocations.

 Thanks Nick!

Signed-off-by: Luke Yang <luke.adi@gmail.com>
Acked-by: Nick Piggin <npiggin@suse.de>

 slab.c |    7 +++++++
 1 files changed, 7 insertions(+)

diff --git a/mm/slab.c b/mm/slab.c
index 4cbf8bb..5a782ff 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1454,7 +1454,14 @@ static void *kmem_getpages(struct kmem_c
        int i;

        flags |= cachep->gfpflags;
+#ifndef CONFIG_MMU
+       /* nommu uses slab's for process anonymous memory allocations, so
+        * requires __GFP_COMP to properly refcount higher order allocations"
+        */
+       page = alloc_pages_node(nodeid, (flags | __GFP_COMP), cachep->gfporder);
+#else
        page = alloc_pages_node(nodeid, flags, cachep->gfporder);
+#endif
        if (!page)
                return NULL;
        addr = page_address(page);

--
Best regards,
Luke Yang,  Kernel for Blackfin maintainer
luke.adi@gmail.com

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diff --git a/mm/slab.c b/mm/slab.c
index 4cbf8bb..5a782ff 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1454,7 +1454,14 @@ static void *kmem_getpages(struct kmem_c
 	int i;
 
 	flags |= cachep->gfpflags;
+#ifndef CONFIG_MMU
+	/* nommu uses slab's for process anonymous memory allocations, so
+	 * requires __GFP_COMP to properly refcount higher order allocations"
+	 */
+	page = alloc_pages_node(nodeid, (flags | __GFP_COMP), cachep->gfporder);
+#else
 	page = alloc_pages_node(nodeid, flags, cachep->gfporder);
+#endif
 	if (!page)
 		return NULL;
 	addr = page_address(page);