Messages in this thread | | | From | Neil Brown <> | Date | Sun, 14 May 2006 21:15:35 +1000 | Subject | Re: [PATCH 008 of 8] md/bitmap: Change md/bitmap file handling to use bmap to file blocks. |
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On Saturday May 13, akpm@osdl.org wrote: > Paul Clements <paul.clements@steeleye.com> wrote: > > > > Andrew Morton wrote: > > > > > The loss of pagecache coherency seems sad. I assume there's never a > > > requirement for userspace to read this file. > > > > Actually, there is. mdadm reads the bitmap file, so that would be > > broken. Also, it's just useful for a user to be able to read the bitmap > > (od -x, or similar) to figure out approximately how much more he's got > > to resync to get an array in-sync. Other than reading the bitmap file, I > > don't know of any way to determine that. > > Read it with O_DIRECT :(
Which is exactly what the next release of mdadm does. As the patch comment said:
: With this approach the pagecache may contain data which is inconsistent with : what is on disk. To alleviate the problems this can cause, md invalidates : the pagecache when releasing the file. If the file is to be examined : while the array is active (a non-critical but occasionally useful function), : O_DIRECT io must be used. And new version of mdadm will have support for this.
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