linux-ext4 - Re: [PATCH 2/2] ext4: Use slab allocator for sub-page sized allocations

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Message-ID: <4B1A0101.4090605@redhat.com>
Date:	Sat, 05 Dec 2009 00:43:13 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
CC:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/2] ext4: Use slab allocator for sub-page sized allocations

Eric Sandeen wrote:
> Theodore Ts'o wrote:
>> Now that the SLUB seems to be fixed so that it respects the requested
>> alignment, use kmem_cache_alloc() to allocator if the block size of
>> the buffer heads to be allocated is less than the page size.
>> Previously, we were using 16k page on a Power system for each buffer,
>> even when the file system was using 1k or 4k block size.
> 
> So, this undoes commit c089d490dfbf53bc0893dc9ef57cf3ee6448314d
> more or less, right:
> 
> JBD: Replace slab allocations with page allocations
> 
> Author: Mingming Cao <cmm@...ibm.com>
> 
> JBD allocate memory for committed_data and frozen_data from slab. However
> JBD should not pass slab pages down to the block layer.
> Use page allocator pages instead. This will also prepare JBD for the large blocksize patchset.
> 
> Was alignment the only reason that commit went in?

Actually, Christoph reminded me that iscsi & co will not like this.

See commit 1fa40b01ae4d1b00e366d4949edcc230f5cd6d99 for xfs moving
in the opposite direction back in 2007...

-Eric
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