Messages in this thread | | | Date | Thu, 5 May 2016 07:27:48 -0700 | From | Christoph Hellwig <> | Subject | Re: [PATCH v5 1/2] dax: Don't touch i_dio_count in dax_do_io() |
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On Thu, May 05, 2016 at 04:16:37PM +0200, Jan Kara wrote: > We cannot easily do this currently - the reason is that in several places we > wait for i_dio_count to drop to 0 (look for inode_dio_wait()) while > holding i_mutex to wait for all outstanding DIO / DAX IO. You'd break this > logic with this patch. > > If we indeed put all writes under i_mutex, this problem would go away but > as Dave explains in his email, we consciously do as much IO as we can > without i_mutex to allow reasonable scalability of multiple writers into > the same file.
So the above should be fine for xfs, but you're telling me that ext4 is doing DAX I/O without any inode lock at all? In that case it's indeed not going to work.
> The downside of that is that overwrites and writes vs reads are not atomic > wrt each other as POSIX requires. It has been that way for direct IO in XFS > case for a long time, with DAX this non-conforming behavior is proliferating > more. I agree that's not ideal but serializing all writes on a file is > rather harsh for persistent memory as well...
For non-O_DIRECT I/O it's simply required..
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