linux-ext4 - Re: [PATCH 1/2] ext4: optimize ext4_ext_convert_to

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Message-ID: <20111027154616.GF31921@thunk.org>
Date:	Thu, 27 Oct 2011 11:46:16 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Eric Gouriou <egouriou@...gle.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/2] ext4: optimize ext4_ext_convert_to_initialized()

On Sun, Sep 25, 2011 at 11:54:28PM -0700, Eric Gouriou wrote:
> This patch introduces a fast path in ext4_ext_convert_to_initialized()
> for the case when the conversion can be performed by transferring
> the newly initialized blocks from the uninitialized extent into
> an adjacent initialized extent. Doing so removes the expensive
> invocations of memmove() which occur during extent insertion and
> the subsequent merge.
> 
> In practice this should be the common case for clients performing
> append writes into files pre-allocated via
> fallocate(FALLOC_FL_KEEP_SIZE). In such a workload performed via
> direct IO and when using a suboptimal implementation of memmove()
> (x86_64 prior to the 2.6.39 rewrite), this patch reduces kernel CPU
> consumption by 32%.
> 
> Two new trace points are added to ext4_ext_convert_to_initialized()
> to offer visibility into its operations. No exit trace point has
> been added due to the multiplicity of return points. This can be
> revisited once the upstream cleanup is backported.
> 
> Signed-off-by: Eric Gouriou <egouriou@...gle.com>

Thanks, applied.

						- Ted
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