On 4/26/25 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>
Reviewed-by: Bernd Schubert <bschubert@xxxxxxx>
> ---
> 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]) {
> + WARN_ON(ap->folios[ap->num_folios - 1] != folio);
> + ap->descs[ap->num_folios - 1].length += len;
> + WARN_ON(ap->descs[ap->num_folios - 1].length > folio_size(folio));
> + } else {
> + offset = start + (folio_page_idx(folio, pages[i]) << PAGE_SHIFT);
> + ap->descs[ap->num_folios].offset = offset;
> + ap->descs[ap->num_folios].length = len;
> + ap->folios[ap->num_folios] = folio;
> + start = 0;
> + ap->num_folios++;
> + prev_folio = folio;
> + }
>
> - ap->descs[ap->num_folios].offset = offset;
> - ap->descs[ap->num_folios].length = len;
> - ap->folios[ap->num_folios] = folio;
> - start = 0;
> ret -= len;
> - ap->num_folios++;
> }
> -
> - nr_pages += nfolios;
> + nr_pages += npages;
> }
> kfree(pages);
>
