Re: upcoming kerneloops.org item: get_page_from_freelist

[Pekka J Enberg]

Hi Ted,

On Thu, Jun 25, 2009 at 05:11:25PM -0500, Eric Sandeen wrote:
> > ecryptfs used to do kmalloc(PAGE_CACHE_SIZE) & virt_to_page on that, and
> > with SLUB + slub debug, that gave back non-aligned memory, causing
> > eventual corruption ...

On Thu, 25 Jun 2009, Theodore Tso wrote:
> Grumble.  Any chance we could add an kmem_cache option which requires
> the memory to be aligned?  Otherwise we could rewrite our own sub-page
> allocator in ext4 that only handled aligned filesystem block sizes
> (i.e., 1k, 2k, 4k, etc.) but that would be really silly and be extra
> code that really should be done once at core functionality.

We alredy have SLAB_HW_ALIGN but I wonder if this is a plain old bug in 
SLUB. Christoph, Nick, don't we need something like this in the allocator? 
Eric, does this fix your case?

			Pekka

diff --git a/mm/slub.c b/mm/slub.c
index 819f056..7cd1e69 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2400,7 +2400,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
 	 * user specified and the dynamic determination of cache line size
 	 * on bootup.
 	 */
-	align = calculate_alignment(flags, align, s->objsize);
+	align = calculate_alignment(flags, align, size);
 
 	/*
 	 * SLUB stores one object immediately after another beginning from
--
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