Re: [PATCHv6 11/11] iomap: add support for dma aligned direct-io

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Jul 22, 2022 at 06:12:40PM +0000, Eric Biggers wrote:
> On Fri, Jul 22, 2022 at 10:53:42AM -0700, Darrick J. Wong wrote:
> > On Fri, Jul 22, 2022 at 12:36:01AM -0700, Eric Biggers wrote:
> > > [+f2fs list and maintainers]
> > > 
> > > On Fri, Jun 10, 2022 at 12:58:30PM -0700, Keith Busch wrote:
> > > > From: Keith Busch <kbusch@kernel.org>
> > > > 
> > > > Use the address alignment requirements from the block_device for direct
> > > > io instead of requiring addresses be aligned to the block size.
> > > > 
> > > > Signed-off-by: Keith Busch <kbusch@kernel.org>
> > > > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > > > ---
> > > >  fs/iomap/direct-io.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> > > > index 370c3241618a..5d098adba443 100644
> > > > --- a/fs/iomap/direct-io.c
> > > > +++ b/fs/iomap/direct-io.c
> > > > @@ -242,7 +242,6 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
> > > >  	struct inode *inode = iter->inode;
> > > >  	unsigned int blkbits = blksize_bits(bdev_logical_block_size(iomap->bdev));
> > > >  	unsigned int fs_block_size = i_blocksize(inode), pad;
> > > > -	unsigned int align = iov_iter_alignment(dio->submit.iter);
> > > >  	loff_t length = iomap_length(iter);
> > > >  	loff_t pos = iter->pos;
> > > >  	unsigned int bio_opf;
> > > > @@ -253,7 +252,8 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
> > > >  	size_t copied = 0;
> > > >  	size_t orig_count;
> > > >  
> > > > -	if ((pos | length | align) & ((1 << blkbits) - 1))
> > > > +	if ((pos | length) & ((1 << blkbits) - 1) ||
> > > > +	    !bdev_iter_is_aligned(iomap->bdev, dio->submit.iter))
> > 
> > How does this change intersect with "make statx() return DIO alignment
> > information" ?  Will the new STATX_DIOALIGN implementations have to be
> > adjusted to set stx_dio_mem_align = bdev_dma_alignment(...)?
> > 
> > I'm guessing the answer is yes, but I haven't seen any patches on the
> > list to do that, but more and more these days email behaves like a flood
> > of UDP traffic... :(
> > 
> 
> Yes.  I haven't done that in the STATX_DIOALIGN patchset yet because I've been
> basing it on upstream, which doesn't yet have this iomap patch.  I haven't been
> expecting STATX_DIOALIGN to make 5.20, given that it's a new UAPI that needs
> time to be properly reviewed, plus I've just been busy with other things.  So
> I've been planning to make the above change after this patch lands upstream.

<nod> Ok, I'm looking forward to it.  Thank you for your work on statx! :)

--D

> - Eric