linux-kernel - Re: [Ext2-devel] [RFC][PATCH] Manage jbd allocations from its own slabs

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Message-ID: <20060825022405.GA3692@thunk.org>
Date:	Thu, 24 Aug 2006 22:24:05 -0400
From:	Theodore Tso <tytso@....edu>
To:	Badari Pulavarty <pbadari@...ibm.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Herbert Xu <herbert@...dor.apana.org.au>, akpm@...l.org,
	lkml <linux-kernel@...r.kernel.org>,
	ext2-devel <Ext2-devel@...ts.sourceforge.net>
Subject: Re: [Ext2-devel] [RFC][PATCH] Manage jbd allocations from its own slabs

On Thu, Aug 24, 2006 at 12:11:25PM -0700, Badari Pulavarty wrote:
> > 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).

Is there some way we can cleanly have a shortcut case where we use
alloc_page() if fs_blocksize == PAGE_SIZE?  The efficiency gains for
what will be the common case on many architectures will probably make
this worthwhile....

						- Ted
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