Re: [RFC][PATCH] Manage jbd allocations from its own slabs
From: Badari Pulavarty
Date: Thu Aug 24 2006 - 15:08:43 EST
Christoph Hellwig wrote:
On Wed, Aug 23, 2006 at 04:08:15PM -0700, Badari Pulavarty wrote:
Hi,
Here is the fix to "bh: Ensure bh fits within a page" problem
caused by JBD.
BTW, I realized that this problem can happen only with 1k, 2k
filesystems - as 4k, 8k allocations disable slab debug
automatically. But for completeness, I created slabs for those
also.
What do you think ? I ran basic tests and things are fine.
Why can't you just use alloc_page? I bet the whole slab overhead
eats more memory than what's wasted when using alloc_pages. Especially
as the typical usecase is a 4k blocks filesystem with 4k pagesize
where the overhead of alloc_page is non-existant.
Yes. That was what proposed earlier. But for 1k, 2k allocations we end
up wasting whole page.
Isn't it ? Thats why I created right sized slabs and disable slab-debug.
I guess, I can do this
only for 1k, 2k filesystems and directly use alloc_page() for 4k and 8k
- but that would make
code ugly and also it doesn't handle cases for bigger base pagesize
systems (64k power).
Thanks,
Badari
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