linux-kernel - Re: [PATCH v2 7/7] fuse: convert direct IO paths to use FOLL

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Message-ID: <CAJfpegvdTqdk9rs-yaEp1aqav4=t9qSpQri7gW8zzb+t7+_88A@mail.gmail.com>
Date:   Wed, 31 Aug 2022 12:37:38 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>, Jan Kara <jack@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 7/7] fuse: convert direct IO paths to use FOLL_PIN

On Wed, 31 Aug 2022 at 06:19, John Hubbard <jhubbard@...dia.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@...dia.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