Messages in this thread | | | Date | Thu, 01 Sep 2011 10:47:31 -0700 | From | Allison Henderson <> | Subject | Re: lock i_mutex for fallocate? |
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On 09/01/2011 12:31 AM, Christoph Hellwig wrote: > On Wed, Aug 31, 2011 at 05:33:25PM -0700, Allison Henderson wrote: >> Hi All, >> >> In ext4 punch hole, we realized that the punch hole operation needs >> to be done under i_mutex just like truncate. i_mutex for truncate >> is held in the vfs layer, so we dont need to lock it at the file >> system layer, but vfs does not lock i_mutex for fallocate. We can >> lock i_mutex for fallocate at the fs layer, but question was raised >> then: should i_mutex for fallocate be held in the vfs layer instead? >> I do not know if other file systems need i_mutex to be locked for >> fallocate, or if they might be locking it already, so I am doing >> some investigating on this idea, and also the appropriate use of >> i_mutex in general. Can someone provide some insight this topic? > > Don't do it. > > i_mutex is already overloaded, and this does not fit into any > of the somewhat reasonable uses cases for it, which are: > > a) for directories the VFS uses it to protect the tree topology > b) for regular files all generic I/O code currently uses it to > serialize writers. > c) the VFS uses it around truncate, and setxattr updates > d) filesystems abuse it for internal metadata in various places > > As you can see right now we do not hold it over any file operation, > and I'm absolutely against adding that. I'd rather untange the > current uses, specificly: > > - push synchronization of setattr into the filesystems > - push synchronization of xattr write operations into the filesystems > - move the read/write synchronization to a separate shared/exclusive > lock like it's already done in XFS, and like Lukas proposed for > ext4. This fixes the Posix compliance corner cases about reads > beeing atomic vs writes, simplifies direct I/O locking a lot, > and allows for more parallel direct I/O support like XFS supports. > - try to get rid of the abuses inside filesystems as much as possible. >
Alrighty, this helps explain things! Thx all for the feedback! :)
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