Re: upcoming kerneloops.org item: get_page_from_freelist

[Eric Sandeen]

Pekka J Enberg wrote:
> 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?

I'll test it; it'd be great if it did, I'm um, a bit ashamed at how I
fixed it ;)

Thanks!
-Eric

> 			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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