Messages in this thread | | | Date | Mon, 23 Jan 2006 14:52:51 +0100 | From | Antonio Vargas <> | Subject | Re: soft update vs journaling? |
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On 1/23/06, Kyle Moffett <mrmacman_g4@mac.com> wrote: > On Jan 23, 2006, at 02:24, Theodore Ts'o wrote: > > Hot-shrinking a filesystem is certainly possible for any > > filesystem, but the problem is how many filesystem data structures > > you have to walk in order to find all the owner of all of the > > blocks that you have to relocate. That generally isn't a RAM > > overhead problem, but the fact that in general, most filesystems > > don't have an efficient way to answer the question, "who owns this > > arbitrary disk block?" Having extents means you have a slightly > > more efficient encoding system, but it still is the case that you > > have to check potentially every file in the filesystem to see if it > > is the owner of one of the disk blocks that needs to be moved when > > you are shrinking the filesystem. > > The way that I'm considering implementing this is by intentionally > fragmenting the allocation bitmap, catalog file, etc, such that each > 1/8 or so of the disk contains its own allocation bitmap describing > its contents, its own set of files or directories, etc. The > allocator would largely try to keep individual btree fragments > cohesive, such that one of the 1/8th divisions of the disk would only > have pertinent data for itself. The idea would be that when trying > to look up an allocation block, in the common case you need only > parse a much smaller subsection of the disk structures.
this sounds exactly the same as ext2/ext3 allocation groups :)
> > And the only use for such a [reverse-mapping] data structure would > > be to make shrinking a filesystem more efficient. > > Not entirely true. I _believe_ you could use such data structures to > make the allocation algorithm much more robust against fragmentation > if you record the right kind of information. > > Cheers, > Kyle Moffett > > -- > If you don't believe that a case based on [nothing] could potentially > drag on in court for _years_, then you have no business playing with > the legal system at all. > -- Rob Landley >
-- Greetz, Antonio Vargas aka winden of network
http://wind.codepixel.com/ windNOenSPAMntw@gmail.com thesameasabove@amigascne.org
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