On Mon 21-08-17 12:58:30, Ross Zwisler wrote:
> On Thu, Aug 17, 2017 at 06:08:13PM +0200, Jan Kara wrote:
> > Add a flag to iomap interface informing the caller that inode needs
> > fdstasync(2) for returned extent to become persistent and use it in DAX
> > fault code so that we map such extents only read only. We propagate the
> > information that the page table entry has been inserted write-protected
> > from dax_iomap_fault() with a new VM_FAULT_RO flag. Filesystem fault
> > handler is then responsible for calling fdatasync(2) and updating page
> > tables to map pfns read-write. dax_iomap_fault() also takes care of
> > updating vmf->orig_pte to match the PTE that was inserted so that we can
> > safely recheck that PTE did not change while write-enabling it.
>
> This changelog needs a little love. s/VM_FAULT_RO/VM_FAULT_NEEDDSYNC/, the
> new path doesn't do the RO mapping, but instead just does the entire RW
> mapping after the fdatasync is complete, the vmf->orig_pte manipulation went
> away, etc.
Yeah, fixed. Thanks for noticing.
> > Signed-off-by: Jan Kara <jack@xxxxxxx>
> > ---
> > fs/dax.c | 31 +++++++++++++++++++++++++++++++
> > include/linux/iomap.h | 2 ++
> > include/linux/mm.h | 6 +++++-
> > 3 files changed, 38 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/dax.c b/fs/dax.c
> > index bc040e654cc9..ca88fc356786 100644
> > --- a/fs/dax.c
> > +++ b/fs/dax.c
> > @@ -1177,6 +1177,22 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf,
> > goto error_finish_iomap;
> > }
> >
> > + /*
> > + * If we are doing synchronous page fault and inode needs fsync,
> > + * we can insert PTE into page tables only after that happens.
> > + * Skip insertion for now and return the pfn so that caller can
> > + * insert it after fsync is done.
> > + */
> > + if (write && (vma->vm_flags & VM_SYNC) &&
> > + (iomap.flags & IOMAP_F_NEEDDSYNC)) {
>
> Just a small nit, but I don't think we really need to check for 'write' here.
> The fact that IOMAP_F_NEEDDSYNC is set tells us that we are doing a write.
>
> if ((flags & IOMAP_WRITE) &&
> !jbd2_transaction_committed(EXT4_SB(inode->i_sb)->s_journal,
> EXT4_I(inode)->i_datasync_tid))
> iomap->flags |= IOMAP_F_NEEDDSYNC;
>
> Ditto for the PMD case.
OK, done.
> With that one simplification and a cleaned up changelog, you can add:
>
> Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Thanks.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
