Re: [RFC][PATCH] Manage jbd allocations from its own slabs

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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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