Re: [PATCH v3 06/10] fuse: convert fuse_do_readpage to use folios

[Josef Bacik <josef@toxicpanda.com>]

On Fri, Sep 27, 2024 at 03:51:17PM -0700, Joanne Koong wrote:
> On Fri, Sep 27, 2024 at 1:54 PM Josef Bacik <josef@toxicpanda.com> wrote:
> >
> > Now that the buffered write path is using folios, convert
> > fuse_do_readpage() to take a folio instead of a page, update it to use
> > the appropriate folio helpers, and update the callers to pass in the
> > folio directly instead of a page.
> >
> > Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> > ---
> >  fs/fuse/file.c | 25 ++++++++++++-------------
> >  1 file changed, 12 insertions(+), 13 deletions(-)
> >
> > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> > index 2af9ec67a8e7..8a4621939d3b 100644
> > --- a/fs/fuse/file.c
> > +++ b/fs/fuse/file.c
> > @@ -858,12 +858,13 @@ static void fuse_short_read(struct inode *inode, u64 attr_ver, size_t num_read,
> >         }
> >  }
> >
> > -static int fuse_do_readpage(struct file *file, struct page *page)
> > +static int fuse_do_readpage(struct file *file, struct folio *folio)
> 
> Should we also rename this to fuse_do_readfolio instead of fuse_do_readpage?
> 
> >  {
> > -       struct inode *inode = page->mapping->host;
> > +       struct inode *inode = folio->mapping->host;
> >         struct fuse_mount *fm = get_fuse_mount(inode);
> > -       loff_t pos = page_offset(page);
> > +       loff_t pos = folio_pos(folio);
> >         struct fuse_page_desc desc = { .length = PAGE_SIZE };
> > +       struct page *page = &folio->page;
> >         struct fuse_io_args ia = {
> >                 .ap.args.page_zeroing = true,
> >                 .ap.args.out_pages = true,
> > @@ -875,11 +876,10 @@ static int fuse_do_readpage(struct file *file, struct page *page)
> >         u64 attr_ver;
> >
> >         /*
> > -        * Page writeback can extend beyond the lifetime of the
> > -        * page-cache page, so make sure we read a properly synced
> > -        * page.
> > +        * Folio writeback can extend beyond the lifetime of the
> > +        * folio, so make sure we read a properly synced folio.
> 
> Is this comment true that folio writeback can extend beyond the
> lifetime of the folio? Or is it that folio writeback can extend beyond
> the lifetime of the folio in the page cache?

This is true today because of the temporary pages.  We can have writebackout for
the range of the folio outstanding because the temporary pages can still be in
flight and we might have reclaimed the folio that existed for that given range.
Once you delete the temporary pages thing the comment will no longer be correct.
I'll update the comment to be more clear, thanks,

Josef