Re: [PATCH v2 7/7] fuse: convert direct IO paths to use FOLL_PIN

Miklos Szeredi
2022-08-31T10:38:11Z

On Wed, 31 Aug 2022 at 06:19, John Hubbard <jhubbard@nvidia.com> wrote:
>
> Convert the fuse filesystem to use pin_user_pages_fast() and
> unpin_user_page(), instead of get_user_pages_fast() and put_page().
>
> The user of pin_user_pages_fast() depends upon:
>
> 1) CONFIG_BLK_USE_PIN_USER_PAGES_FOR_DIO, and
>
> 2) User-space-backed pages or ITER_BVEC pages.
>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
> fs/fuse/dev.c | 11 +++++++++--
> fs/fuse/file.c | 32 +++++++++++++++++++++-----------
> fs/fuse/fuse_i.h | 1 +
> 3 files changed, 31 insertions(+), 13 deletions(-)
>
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index 51897427a534..5de98a7a45b1 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -675,7 +675,12 @@ static void fuse_copy_finish(struct fuse_copy_state *cs)
> flush_dcache_page(cs->pg);
> set_page_dirty_lock(cs->pg);
> }
> - put_page(cs->pg);
> + if (!cs->pipebufs &&
> + (user_backed_iter(cs->iter) || iov_iter_is_bvec(cs->iter)))
> + dio_w_unpin_user_page(cs->pg);
> +
> + else
> + put_page(cs->pg);

Why not move the logic into a helper and pass a "bool pinned" argument?

> }
> cs->pg = NULL;
> }
> @@ -730,7 +735,9 @@ static int fuse_copy_fill(struct fuse_copy_state *cs)
> }
> } else {
> size_t off;
> - err = iov_iter_get_pages2(cs->iter, &page, PAGE_SIZE, 1, &off);
> +
> + err = dio_w_iov_iter_pin_pages(cs->iter, &page, PAGE_SIZE, 1,
> + &off);
> if (err < 0)
> return err;
> BUG_ON(!err);
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 1a3afd469e3a..01da38928d0b 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -625,14 +625,19 @@ void fuse_read_args_fill(struct fuse_io_args *ia, struct file *file, loff_t pos,
> }
>
> static void fuse_release_user_pages(struct fuse_args_pages *ap,
> - bool should_dirty)
> + bool should_dirty, bool is_user_or_bvec)
> {
> unsigned int i;
>
> - for (i = 0; i < ap->num_pages; i++) {
> - if (should_dirty)
> - set_page_dirty_lock(ap->pages[i]);
> - put_page(ap->pages[i]);
> + if (is_user_or_bvec) {
> + dio_w_unpin_user_pages_dirty_lock(ap->pages, ap->num_pages,
> + should_dirty);
> + } else {
> + for (i = 0; i < ap->num_pages; i++) {
> + if (should_dirty)
> + set_page_dirty_lock(ap->pages[i]);
> + put_page(ap->pages[i]);
> + }

Same here.

> }
> }
>
> @@ -733,7 +738,7 @@ static void fuse_aio_complete_req(struct fuse_mount *fm, struct fuse_args *args,
> struct fuse_io_priv *io = ia->io;
> ssize_t pos = -1;
>
> - fuse_release_user_pages(&ia->ap, io->should_dirty);
> + fuse_release_user_pages(&ia->ap, io->should_dirty, io->is_user_or_bvec);
>
> if (err) {
> /* Nothing */
> @@ -1414,10 +1419,10 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
> while (nbytes < *nbytesp && ap->num_pages < max_pages) {
> unsigned npages;
> size_t start;
> - ret = iov_iter_get_pages2(ii, &ap->pages[ap->num_pages],
> - *nbytesp - nbytes,
> - max_pages - ap->num_pages,
> - &start);
> + ret = dio_w_iov_iter_pin_pages(ii, &ap->pages[ap->num_pages],
> + *nbytesp - nbytes,
> + max_pages - ap->num_pages,
> + &start);
> if (ret < 0)
> break;
>
> @@ -1483,6 +1488,10 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
> fl_owner_t owner = current->files;
> size_t nbytes = min(count, nmax);
>
> + /* For use in fuse_release_user_pages(): */
> + io->is_user_or_bvec = user_backed_iter(iter) ||
> + iov_iter_is_bvec(iter);
> +

How about io->is_pinned? And a iov_iter_is_pinned() helper?

Thanks,
Miklos