linux-kernel - Re: [PATCH] JBD slab cleanups

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Message-ID: <20070917193443.GA32013@infradead.org>
Date:	Mon, 17 Sep 2007 20:34:43 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	Mingming Cao <cmm@...ibm.com>
Cc:	Christoph Hellwig <hch@...radead.org>, pbadari@...ibm.com,
	Christoph Lameter <clameter@....com>,
	linux-fsdevel@...r.kernel.org,
	ext4 development <linux-ext4@...r.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] JBD slab cleanups

On Mon, Sep 17, 2007 at 12:29:51PM -0700, Mingming Cao wrote:
> The problem with this patch, as Andreas Dilger pointed today in ext4
> interlock call, for 1k,2k block size ext2/3/4, get_free_pages() waste
> 1/3-1/2 page space. 
> 
> What was the originally intention to set up slabs for committed_data(and
> frozen_buffer) in JBD? Why not using kmalloc?

kmalloc is using slabs :)

The intent was to avoid the wasted memory, but as we've repeated a gazillion
times wasted memory on a rather rare codepath doesn't really matter when
you just crash random storage drivers otherwise.
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