linux-ext4 - Re: Potential bug in mballoc --- reusing data blocks before txn commit

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Date:	Tue, 30 Sep 2008 08:35:21 +0400
From:	Alex Tomas <bzzz@....com>
To:	Theodore Tso <tytso@....edu>
Cc:	Andreas Dilger <adilger@....com>, linux-ext4@...r.kernel.org
Subject: Re: Potential bug in mballoc --- reusing data blocks before txn	commit

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

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