Re: [PATCH 2/6] mm/page_io: use a folio in sio_read_complete()

[zhangpeng (AS)]

On 2023/7/17 21:40, Matthew Wilcox wrote:

> On Mon, Jul 17, 2023 at 09:25:58PM +0800, Peng Zhang wrote:
> > +++ b/mm/page_io.c
> > @@ -406,19 +406,19 @@ static void sio_read_complete(struct kiocb *iocb, long ret)
> >   
> >   	if (ret == sio->len) {
> >   		for (p = 0; p < sio->pages; p++) {
> > -			struct page *page = sio->bvec[p].bv_page;
> > +			struct folio *folio = page_folio(sio->bvec[p].bv_page);
> >   
> > -			SetPageUptodate(page);
> > -			unlock_page(page);
> > +			folio_mark_uptodate(folio);
> > +			folio_unlock(folio);
> >   		}
> I'm kind of shocked this works today.  Usually bvecs coalesce adjacent
> pages into a single entry, so you need to use a real iterator like
> bio_for_each_folio_all() to extract individual pages from a bvec.
> Maybe the sio bvec is constructed inefficiently.
>
> I think Kent had some bvec folio iterators in progress?

I'll convert bio_first_page_all() to bio_first_folio_all() in a v2.

> >   		count_vm_events(PSWPIN, sio->pages);
> >   	} else {
> >   		for (p = 0; p < sio->pages; p++) {
> > -			struct page *page = sio->bvec[p].bv_page;
> > +			struct folio *folio = page_folio(sio->bvec[p].bv_page);
> >   
> > -			SetPageError(page);
> > -			ClearPageUptodate(page);
> > -			unlock_page(page);
> > +			folio_set_error(folio);
> > +			folio_clear_uptodate(folio);
> > +			folio_unlock(folio);
> Similar questions to the last patch -- who checks the error flag on this
> page/folio, and isn't the folio already !uptodate?

Yes, the folio is already !uptodate. I'll drop this line.
Maybe wait_dev_supers() in fs/btrfs/disk-io.c checks the PageError()?

> >   		}
> >   		pr_alert_ratelimited("Read-error on swap-device\n");
> >   	}
> > --
> > 2.25.1
--
Best Regards,
Peng