On Fri 23-07-21 22:58:40, Andreas Gruenbacher wrote:
> Also disable page faults during direct I/O requests and implement the same
> kind
> of retry logic as in the buffered I/O case.
>
> Direct I/O requests differ from buffered I/O requests in that they use
> bio_iov_iter_get_pages for grabbing page references and faulting in pages
> instead of triggering real page faults. Those manual page faults can be
> disabled with the iocb->noio flag.
>
> Signed-off-by: Andreas Gruenbacher <agrue...@redhat.com>
> ---
> fs/gfs2/file.c | 34 +++++++++++++++++++++++++++++++++-
> 1 file changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
> index f66ac7f56f6d..7986f3be69d2 100644
> --- a/fs/gfs2/file.c
> +++ b/fs/gfs2/file.c
> @@ -782,21 +782,41 @@ static ssize_t gfs2_file_direct_read(struct kiocb
> *iocb, struct iov_iter *to,
> struct file *file = iocb->ki_filp;
> struct gfs2_inode *ip = GFS2_I(file->f_mapping->host);
> size_t count = iov_iter_count(to);
> + size_t written = 0;
> ssize_t ret;
>
> + /*
> + * In this function, we disable page faults when we're holding the
> + * inode glock while doing I/O. If a page fault occurs, we drop the
> + * inode glock, fault in the pages manually, and then we retry. Other
> + * than in gfs2_file_read_iter, iomap_dio_rw can trigger implicit as
> + * well as manual page faults, and we need to disable both kinds
> + * separately.
> + */
> +
> if (!count)
> return 0; /* skip atime */
>
> gfs2_holder_init(ip->i_gl, LM_ST_DEFERRED, 0, gh);
> +retry:
> ret = gfs2_glock_nq(gh);
> if (ret)
> goto out_uninit;
>
> + pagefault_disable();
Is there any use in pagefault_disable() here? iomap_dio_rw() should not
trigger any page faults anyway, should it?
Honza
--
Jan Kara <j...@suse.com>
SUSE Labs, CR
