Re: [PATCH 17/17] xfs: support for synchronous DAX faults
On Fri 27-10-17 08:43:01, Christoph Hellwig wrote:
On Thu, Oct 26, 2017 at 05:48:04PM +0200, Jan Kara wrote:
> But now that I look at XFS implementation again, it misses handling
> of VM_FAULT_NEEDSYNC in xfs_filemap_pfn_mkwrite() (ext4 gets this right).
> I'll fix this by using __xfs_filemap_fault() for xfs_filemap_pfn_mkwrite()
> as well since it mostly duplicates it anyway... Thanks for inquiring!
My first patches move xfs_filemap_pfn_mkwrite to use __xfs_filemap_fault,
but that didn't work. Wish I'd remember why, though.
Maybe due to the additional check on IS_DAX(inode) in __xfs_filemap_fault()
which could do the wrong thing if per-inode DAX flag is switched? Because
otherwise __xfs_filemap_fault(vmf, PE_SIZE_PTE, true) does exactly the same
thing as xfs_filemap_pfn_mkwrite() did.
If we do care about per-inode DAX flag switching, I can just fixup
xfs_filemap_pfn_mkwrite() but my understanding was that we ditched the idea
at least until someone comes up with a reliable way to implement that...
Honza
--
Jan Kara <jack(a)suse.com>
SUSE Labs, CR