On Fri, Jul 4, 2025 at 3:24 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> On 26.04.25 02:08, Joanne Koong wrote:
> > Optimize processing folios larger than one page size for the direct io
> > case. If contiguous pages are part of the same folio, collate the
> > processing instead of processing each page in the folio separately.
> >
> > Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
> > Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > ---
> > fs/fuse/file.c | 55 +++++++++++++++++++++++++++++++++++++-------------
> > 1 file changed, 41 insertions(+), 14 deletions(-)
> >
> > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> > index 9a31f2a516b9..61eaec1c993b 100644
> > --- a/fs/fuse/file.c
> > +++ b/fs/fuse/file.c
> > @@ -1490,7 +1490,8 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
> > }
> >
> > while (nbytes < *nbytesp && nr_pages < max_pages) {
> > - unsigned nfolios, i;
> > + struct folio *prev_folio = NULL;
> > + unsigned npages, i;
> > size_t start;
> >
> > ret = iov_iter_extract_pages(ii, &pages,
> > @@ -1502,23 +1503,49 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
> >
> > nbytes += ret;
> >
> > - nfolios = DIV_ROUND_UP(ret + start, PAGE_SIZE);
> > + npages = DIV_ROUND_UP(ret + start, PAGE_SIZE);
> >
> > - for (i = 0; i < nfolios; i++) {
> > - struct folio *folio = page_folio(pages[i]);
> > - unsigned int offset = start +
> > - (folio_page_idx(folio, pages[i]) << PAGE_SHIFT);
> > - unsigned int len = min_t(unsigned int, ret, PAGE_SIZE - start);
> > + /*
> > + * We must check each extracted page. We can't assume every page
> > + * in a large folio is used. For example, userspace may mmap() a
> > + * file PROT_WRITE, MAP_PRIVATE, and then store to the middle of
> > + * a large folio, in which case the extracted pages could be
> > + *
> > + * folio A page 0
> > + * folio A page 1
> > + * folio B page 0
> > + * folio A page 3
> > + *
> > + * where folio A belongs to the file and folio B is an anonymous
> > + * COW page.
> > + */
> > + for (i = 0; i < npages && ret; i++) {
> > + struct folio *folio;
> > + unsigned int offset;
> > + unsigned int len;
> > +
> > + WARN_ON(!pages[i]);
> > + folio = page_folio(pages[i]);
> > +
> > + len = min_t(unsigned int, ret, PAGE_SIZE - start);
> > +
> > + if (folio == prev_folio && pages[i] != pages[i - 1]) {
>
> I don't really understand the "pages[i] != pages[i - 1]" part.
>
> Why would you have to equal page pointers in there?
>
The pages extracted are user pages from a userspace iovec. AFAICT,
there's the possibility, eg if userspace mmaps() the file with
copy-on-write, that the same physical page could back multiple
contiguous virtual addresses.
>
> Something that might be simpler to understand and implement would be using
>
> num_pages_contiguous()
>
> from
>
> https://lore.kernel.org/all/20250704062602.33500-2-lizhe.67@xxxxxxxxxxxxx/T/#u
>
> and then just making sure that we don't exceed the current folio, if we
> ever get contiguous pages that cross a folio.
Thanks for the link. I think here it's common that the pages array
would hold pages from multiple different folios, so maybe a new helper
num_pages_contiguous_folio() would be useful to return back the number
of contiguous pages that are within the scope of the same folio.
Thanks,
Joanne
>
>
> --
> Cheers,
>
> David / dhildenb
>
