linux-ext4 - Re: upcoming kerneloops.org item: get_page_from

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Message-ID: <4A43F60D.2040801@redhat.com>
Date:	Thu, 25 Jun 2009 17:11:25 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Theodore Tso <tytso@....edu>, Andreas Dilger <adilger@....com>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	penberg@...helsinki.fi, arjan@...radead.org,
	linux-kernel@...r.kernel.org, cl@...ux-foundation.org,
	npiggin@...e.de, linux-ext4@...r.kernel.org
Subject: Re: upcoming kerneloops.org item: get_page_from_freelist

Theodore Tso wrote:
> On Thu, Jun 25, 2009 at 11:26:28PM +0200, Andreas Dilger wrote:
>> IIRC there was also a good reason for this in the past, related to
>> the buffers being submitted to the block device layer, and if they
>> were allocated from the slab cache with CONFIG_DEBUG_SLAB or something
>> similar enabled the buffer would be misaligned and cause grief.
> 
> So what does SLAB/SLUB/SLOB do if we create a slab cache which is a
> power of two?  Can one of the allocators still return misaligned
> blocks of memory in some circumstances?
> 
> 						- Ted

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 ...

-Eric

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