Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has BDI_CAP_SYNC capability

Matthew Wilcox
2017-08-09T02:31:22Z

On Wed, Aug 09, 2017 at 10:51:13AM +0900, Minchan Kim wrote:
> On Tue, Aug 08, 2017 at 06:29:04AM -0700, Matthew Wilcox wrote:
> > On Tue, Aug 08, 2017 at 05:49:59AM -0700, Matthew Wilcox wrote:
> > > + struct bio sbio;
> > > + struct bio_vec sbvec;
> >
> > ... this needs to be sbvec[nr_pages], of course.
> >
> > > - bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
> > > + if (bdi_cap_synchronous_io(inode_to_bdi(inode))) {
> > > + bio = &sbio;
> > > + bio_init(bio, &sbvec, nr_pages);
> >
> > ... and this needs to be 'sbvec', not '&sbvec'.
>
> I don't get it why we need sbvec[nr_pages].
> On-stack-bio works with per-page.
> May I miss something?

The way I redid it, it will work with an arbitrary number of pages.

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