linux-ext4 - Re: [PATCH v2] ext4: remove the entry from es tree when bigalloc is enabled

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Date:	Mon, 29 Jul 2013 19:50:47 +0200
From:	Jan Kara <jack@...e.cz>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Zheng Liu <gnehzuil.liu@...il.com>, linux-ext4@...r.kernel.org,
	Jan Kara <jack@...e.cz>, Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [PATCH v2] ext4: remove the entry from es tree when bigalloc is
 enabled

On Mon 29-07-13 12:21:51, Ted Tso wrote:
> On Fri, Jul 26, 2013 at 07:42:06AM +0800, Zheng Liu wrote:
> > From: Jan Kara <jack@...e.cz>
> > 
> > Now in ext4_da_page_release_reservation() we remove the entry from es
> > tree if to_release != 0.  But there are two issues.  One is that it is
> > wrong when blocksize != pagesize,
> 
> The commit description says that this is wrong, but I don't see
> anything in the patch which addresses this.  And could you state what
> the impact is of this wrongness?
  Well, this wrongness actually shouldn't have any real impact - for
blocksize < pagesize the extent tree isn't used while truncate_pagecache()
is running and ext4_truncate() then removes the whole truncated range from
the tree again which hides any problems in
ext4_da_page_release_reservation(). When bigalloc is used, we use the
extent tree during truncate_pagecache() but to_release is always == 1 and
thus the problem doesn't exist.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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