linux-ext4 - Re: [PATCH 42/74] libext2fs: only punch complete clusters

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Message-ID: <20131216045259.GE28536@thunk.org>
Date:	Sun, 15 Dec 2013 23:52:59 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	linux-ext4@...r.kernel.org, Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [PATCH 42/74] libext2fs: only punch complete clusters

On Tue, Dec 10, 2013 at 05:22:59PM -0800, Darrick J. Wong wrote:
> When bigalloc is enabled, using ext2fs_block_alloc_stats2() to free
> any block in a cluster has the effect of freeing the entire cluster.
> This is problematic if a caller instructs us to punch, say, blocks
> 12-15 of a 16-block cluster, because blocks 0-11 now point to a "free"
> cluster.
> 
> The naive way to solve this problem is to see if any of the other
> blocks in this logical cluster map to a physical cluster.  If so, then
> we know that the cluster is still in use and it mustn't be freed.
> Otherwise, we are punching the last mapped block in this cluster, so
> we can free the cluster.
> 
> The implementation given only does the rigorous checks for the partial
> clusters at the beginning and end of the punching range.
> 
> v2: Refactor the block free code into a separate helper function that
> should be more efficient.
> 
> Reviewed-by: Zheng Liu <wenqing.lz@...bao.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>

Thanks, applied.

						- Ted
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