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

From	Minchan Kim <minchan@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has BDI_CAP_SYNC capability
Date	2017-08-10 06:10 +0200
Message-ID	<ucMXf-qS-1@gated-at.bofh.it> (permalink)
References	(3 earlier) <uccK5-va-1@gated-at.bofh.it> <ucorT-8tL-1@gated-at.bofh.it> <ucpei-Kz-9@gated-at.bofh.it> <ucpei-Kz-7@gated-at.bofh.it> <ucM1b-8i7-11@gated-at.bofh.it>
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On Wed, Aug 09, 2017 at 08:04:33PM -0700, Matthew Wilcox wrote:
> On Wed, Aug 09, 2017 at 11:41:50AM +0900, Minchan Kim wrote:
> > On Tue, Aug 08, 2017 at 07:31:22PM -0700, Matthew Wilcox wrote:
> > > 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.
> > 
> > IIUC, it would be good things with dynamic bio alloction with passing
> > allocated bio back and forth but on-stack bio cannot work like that.
> > It should be done in per-page so it is worth?
> 
> I'm not passing the bio back and forth between do_mpage_readpage() and
> its callers.  The version I sent allows for multiple pages in a single
> on-stack bio (when called from mpage_readpages()).

I'm confused. I want to confirm your thought before respinning.
Please correct me if I miss something.

The version you sent to me used on-stack bio within do_mpage_readpage
so that's why I said sbvec[nr_pages] would be pointless because it
works with per-page base unless if we use dynamic bio allocation.

But I guess now you suggest to use on-stack bio in mpage_readpages so
single on-stack bio in mpage_readpages's stack can batch multiple pages
in bvecs of a bio.

Right?

Thread

[PATCH v1 2/6] fs: use on-stack-bio if backing device has BDI_CAP_SYNC capability Minchan Kim <minchan@kernel.org> - 2017-08-08 09:00 +0200
  Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has  BDI_CAP_SYNC capability Matthew Wilcox <willy@infradead.org> - 2017-08-08 15:00 +0200
    Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has  BDI_CAP_SYNC capability Matthew Wilcox <willy@infradead.org> - 2017-08-08 15:30 +0200
      Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has  BDI_CAP_SYNC capability Minchan Kim <minchan@kernel.org> - 2017-08-09 04:00 +0200
        Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has  BDI_CAP_SYNC capability Minchan Kim <minchan@kernel.org> - 2017-08-09 04:50 +0200
          Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has  BDI_CAP_SYNC capability Matthew Wilcox <willy@infradead.org> - 2017-08-10 05:10 +0200
            Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has  BDI_CAP_SYNC capability Dan Williams <dan.j.williams@intel.com> - 2017-08-10 05:10 +0200
              Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has         BDI_CAP_SYNC capability Christoph Hellwig <hch@lst.de> - 2017-08-11 12:50 +0200
                Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has  BDI_CAP_SYNC capability Jens Axboe <axboe@kernel.dk> - 2017-08-11 16:30 +0200
            Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has  BDI_CAP_SYNC capability Minchan Kim <minchan@kernel.org> - 2017-08-10 06:10 +0200
        Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has  BDI_CAP_SYNC capability Matthew Wilcox <willy@infradead.org> - 2017-08-09 05:40 +0200
    Re: [PATCH v1 2/6] fs: use on-stack-bio if backing device has  BDI_CAP_SYNC capability Minchan Kim <minchan@kernel.org> - 2017-08-09 03:50 +0200

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