On Thu, Sep 07, 2017 at 01:54:45PM -0700, Dan Williams wrote: > On Wed, Sep 6, 2017 at 10:07 AM, Ross Zwisler > <ross.zwisler@xxxxxxxxxxxxxxx> wrote: > > On Tue, Sep 05, 2017 at 09:12:35PM -0500, Eric Sandeen wrote: > >> On 9/5/17 5:35 PM, Ross Zwisler wrote: > >> > The original intent of this series was to add a per-inode DAX flag to ext4 > >> > so that it would be consistent with XFS. In my travels I found and fixed > >> > several related issues in both ext4 and XFS. > >> > >> Hi Ross - > >> > >> hch had a lot of reasons to nuke the dax flag from orbit, and we just > >> /disabled/ it in xfs due to its habit of crashing the kernel... > > > > Ah, sorry, I wasn't CC'd on those threads and missed them. For any interested > > bystanders: > > > > https://www.spinics.net/lists/linux-ext4/msg57840.html > > https://www.spinics.net/lists/linux-xfs/msg09831.html > > https://www.spinics.net/lists/linux-xfs/msg10124.html > > > >> so a couple questions: > >> > >> 1) does this series pass hch's "test the per-inode DAX flag" fstest? > > > > Nope, it has the exact same problems as the XFS per-inode DAX flag. > > > >> 2) do we have an agreement that we need this flag at all, or is this > >> just a parity item because xfs has^whad a per-inode flag? > > > > It was for parity, and because it allows admins finer grained control over > > their system. Basically all things discussed in response to Lukas's original > > patch in the first link above. > > I think it's more than parity. When pmem is slower than page cache it > is actively harmful to have DAX enabled globally for a filesystem. So, > not only should we push for per-inode DAX control, we should also push > to deprecate the mount option. I agree with Christoph that we should > try to automatically and transparently enable DAX where it makes > sense, but we also need a finer-grained mechanism than a mount flag to > force the behavior one way or the other. Yep, agreed. I'll play with how to make this work after I've sorted out all the data corruptions I've found. :)
