From: Alex Tomas <bzzz@sun.com>
Subject: Re: Potential bug in mballoc --- reusing data blocks before txn	commit
Date: Tue, 30 Sep 2008 08:35:21 +0400
Message-ID: <48E1AC89.6050803@sun.com>
References: <E1KjlCM-0002L7-SO@closure.thunk.org> <48E138B2.8080707@sun.com>
 <20080929205712.GH10831@mit.edu>
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Cc: Andreas Dilger <adilger@sun.com>, linux-ext4@vger.kernel.org
To: Theodore Tso <tytso@mit.edu>
In-reply-to: <20080929205712.GH10831@mit.edu>
Sender: linux-ext4-owner@vger.kernel.org

Theodore Tso wrote:
> Yeah, I know Andrian Bunk strikes again....  but the right answer is
> to ressurect that code and add it back.

indeed

> Well, we need to keep this information for the SSD Trim command
> anyway; so probably the right approach is to keep a red/black tree of
> extents that need to be freed, and then when the commit callback is
> called, we can update the appropriate mballoc data structures and call
> the SSD trim command if necessary.

why we need a tree? at least for the purpose of keeping blocks unavailable
we'd need just a list as at commit we free them all.

> The other thing which I should check is that if we are using this
> scheme, I think we shouldn't need to keep the shadow copy of the block
> bitmap buffers any more.  I would imagine we still need them for the
> inode bitmaps, for the same reason, though.

shadow copy holds preallocated blocks

thanks, Alex