From: Mitchell Blank Jr <mitch@sfgoth.com>
To: "Theodore Ts'o" <tytso@mit.edu>,
Kyle Moffett <mrmacman_g4@mac.com>,
John Richard Moser <nigelenki@comcast.net>,
linux-kernel@vger.kernel.org
Subject: Re: soft update vs journaling?
Date: Mon, 23 Jan 2006 05:31:40 -0800 [thread overview]
Message-ID: <20060123133140.GG61823@gaz.sfgoth.com> (raw)
In-Reply-To: <20060123072447.GA8785@thunk.org>
Theodore Ts'o wrote:
> in general, most filesystems don't have an efficient way to
> answer the question, "who owns this arbitrary disk block?"
[...]
> Given that this is generally not a common operation, it seems unlikely
> that a filesystem designer would choose to make this particular
> tradeoff.
True -- a much more rational approach would be to provide a translation
table for "old block #" to "new block #" -- then when the filesystem sees
a reference to an invalid blocknumber (>= the filesystem size) it can just
translate it to its new location.
You have to be careful if the filesystem is regrown since some of those
block numbers may now be valid again. It can easily be handled by just
moving the data back to its original block # and removing the mapping.
This doesn't completely remove the extra cost on the block allocator
fastpath: if an block is freed it must make sure to remove any entry pointing
to it from the translation table or you can't handle regrowth properly
(the block could have been reused by a file pointing to the real block # --
you won't know whether to move it back or not). However, this is probably
a lot cheaper than maintaining a full reverse-map, plus you only have to
take it after a shrink has actually happened.
-Mitch
next prev parent reply other threads:[~2006-01-23 13:31 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-22 6:42 soft update vs journaling? John Richard Moser
2006-01-22 8:51 ` Jan Engelhardt
2006-01-22 18:40 ` John Richard Moser
2006-01-22 19:05 ` Adrian Bunk
2006-01-22 19:08 ` Arjan van de Ven
2006-01-22 19:25 ` Adrian Bunk
2006-01-24 2:33 ` Jörn Engel
2006-01-22 9:31 ` Theodore Ts'o
2006-01-22 18:54 ` John Richard Moser
2006-01-22 21:02 ` Theodore Ts'o
2006-01-22 22:44 ` Kyle Moffett
2006-01-23 7:24 ` Theodore Ts'o
2006-01-23 13:31 ` Mitchell Blank Jr [this message]
2006-01-23 13:33 ` Kyle Moffett
2006-01-23 13:52 ` Antonio Vargas
2006-01-23 16:48 ` Linux VFS architecture questions Kyle Moffett
2006-01-23 17:00 ` Pekka Enberg
2006-01-23 17:50 ` Kyle Moffett
2006-01-23 17:54 ` Randy.Dunlap
2006-01-23 20:48 ` soft update vs journaling? Folkert van Heusden
2006-01-23 1:02 ` John Richard Moser
2006-01-22 19:50 ` Diego Calleja
2006-01-22 20:39 ` Suleiman Souhlal
2006-01-22 20:50 ` Diego Calleja
2006-01-23 1:00 ` John Richard Moser
2006-01-23 1:09 ` Suleiman Souhlal
2006-01-23 2:09 ` John Richard Moser
2006-01-22 19:26 ` James Courtier-Dutton
2006-01-23 0:06 ` John Richard Moser
2006-01-23 5:32 ` Michael Loftis
2006-01-23 18:52 ` John Richard Moser
2006-01-23 19:32 ` Matthias Andree
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