Re: [PATCH v4 2/2] block,iomap: disable iopoll when split needed

[Christoph Hellwig <hch@infradead.org>]

On Fri, Nov 20, 2020 at 06:06:54PM +0800, JeffleXu wrote:
> 
> On 11/20/20 1:55 AM, Christoph Hellwig wrote:
> > > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> > > index 933f234d5bec..396ac0f91a43 100644
> > > --- a/fs/iomap/direct-io.c
> > > +++ b/fs/iomap/direct-io.c
> > > @@ -309,6 +309,16 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
> > >   		copied += n;
> > >   		nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
> > > +		/*
> > > +		 * The current dio needs to be split into multiple bios here.
> > > +		 * iopoll for split bio will cause subtle trouble such as
> > > +		 * hang when doing sync polling, while iopoll is initially
> > > +		 * for small size, latency sensitive IO. Thus disable iopoll
> > > +		 * if split needed.
> > > +		 */
> > > +		if (nr_pages)
> > > +			dio->iocb->ki_flags &= ~IOCB_HIPRI;
> > I think this is confusing two things.
> 
> Indeed there's two level of split concerning this issue when doing sync
> iopoll.
> 
> 
> The first is that one bio got split in block-core, and patch 1 of this patch
> set just fixes this.
> 
> 
> Second is that one dio got split into multiple bios in fs layer, and patch 2
> fixes this.
> 
> 
> >   One is that we don't handle
> > polling well when there are multiple bios.  For this I think we should
> > only call bio_set_polled when we know there is a single bio.
> 
> 
> How about the following patch:
> 
> 
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -60,12 +60,12 @@ int iomap_dio_iopoll(struct kiocb *kiocb, bool spin)
> ??EXPORT_SYMBOL_GPL(iomap_dio_iopoll);
> 
> ??static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap
> *iomap,
> -???????????????????????????? struct bio *bio, loff_t pos)
> +???????????????????????????? struct bio *bio, loff_t pos, bool split)

This seems pretty messed up by your mailer and I have a hard time
reading it.  Can you resend it?