On Wed, Oct 20, 2021 at 10:52:38AM +0800, JeffleXu wrote:
>
>
> On 10/18/21 10:10 PM, Vivek Goyal wrote:
> > On Mon, Oct 11, 2021 at 11:00:47AM +0800, Jeffle Xu wrote:
> >> We add 'always', 'never', and 'inode' (default). '-o dax' continues to
> >> operate the same which is equivalent to 'always'. To be consistemt with
> >> ext4/xfs's tri-state mount option, when neither '-o dax' nor '-o dax='
> >> option is specified, the default behaviour is equal to 'inode'.
> >
> > Hi Jeffle,
> >
> > I am not sure when -o "dax=inode" is used as a default? If user
> > specifies, "-o dax" then it is equal to "-o dax=always", otherwise
> > user will explicitly specify "-o dax=always/never/inode". So when
> > is dax=inode is used as default?
>
> That means when neither '-o dax' nor '-o dax=always/never/inode' is
> specified, it is actually equal to '-o dax=inode', which is also how
> per-file DAX on ext4/xfs works.
[ CC dave chinner]
Is it not change of default behavior for ext4/xfs as well. My
understanding is that prior to this new dax options, "-o dax" enabled
dax on filesystem and if user did not specify it, DAX is disbaled
by default.
Now after introduction of "-o dax=always/never/inode", if suddenly
"-o dax=inode" became the default if user did not specify anything,
that's change of behavior. Is that intentional. If given a choice,
I would rather not change default and ask user to opt-in for
appropriate dax functionality.
Dave, you might have thoughts on this. It makes me uncomfortable to
change virtiofs dax default now just because other filesytems did it.
Thanks
Vivek
>
> This default behaviour for local filesystem, e.g. ext4/xfs, may be
> straightforward, since the disk inode will be read into memory during
> the inode instantiation, and checking for persistent inode attribute
> shall be realatively cheap, except that the default behaviour has
> changed from 'dax=never' to 'dax=inode'.
>
> Come back to virtiofs, when neither '-o dax' nor '-o
> dax=always/never/inode' is specified, and it actually behaves as '-o
> dax=inode', as long as '-o dax=server/attr' option is not specified for
> virtiofsd, virtiofsd will always clear FUSE_ATTR_DAX and thus guest will
> always disable DAX. IOWs, the guest virtiofs atually behaves as '-o
> dax=never' when neither '-o dax' nor '-o dax=always/never/inode' is
> specified, and '-o dax=server/attr' option is not specified for virtiofsd.
>
> But I'm okay if we need to change the default behaviour for virtiofs.
>
>
> >
> >>
> >> By the time this patch is applied, 'inode' mode is actually equal to
> >> 'always' mode, before the per-file DAX flag is introduced in the
> >> following patch.
> >>
> >> Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
> >> ---
> >> fs/fuse/dax.c | 19 ++++++++++++++++---
> >> fs/fuse/fuse_i.h | 14 ++++++++++++--
> >> fs/fuse/inode.c | 10 +++++++---
> >> fs/fuse/virtio_fs.c | 16 ++++++++++++++--
> >> 4 files changed, 49 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
> >> index 1eb6538bf1b2..4c6c64efc950 100644
> >> --- a/fs/fuse/dax.c
> >> +++ b/fs/fuse/dax.c
> >> @@ -1284,11 +1284,14 @@ static int fuse_dax_mem_range_init(struct fuse_conn_dax *fcd)
> >> return ret;
> >> }
> >>
> >> -int fuse_dax_conn_alloc(struct fuse_conn *fc, struct dax_device *dax_dev)
> >> +int fuse_dax_conn_alloc(struct fuse_conn *fc, enum fuse_dax_mode dax_mode,
> >> + struct dax_device *dax_dev)
> >> {
> >> struct fuse_conn_dax *fcd;
> >> int err;
> >>
> >> + fc->dax_mode = dax_mode;
> >> +
> >> if (!dax_dev)
> >> return 0;
> >>
> >> @@ -1335,11 +1338,21 @@ static const struct address_space_operations fuse_dax_file_aops = {
> >> static bool fuse_should_enable_dax(struct inode *inode)
> >> {
> >> struct fuse_conn *fc = get_fuse_conn(inode);
> >> + unsigned int dax_mode = fc->dax_mode;
> >> +
> >> + if (dax_mode == FUSE_DAX_NEVER)
> >> + return false;
> >>
> >> - if (fc->dax)
> >> + /*
> >> + * If 'dax=always/inode', fc->dax couldn't be NULL even when fuse
> >> + * daemon doesn't support DAX, since the mount routine will fail
> >> + * early in this case.
> >> + */
> >> + if (dax_mode == FUSE_DAX_ALWAYS)
> >> return true;
> >>
> >> - return false;
> >> + /* dax_mode == FUSE_DAX_INODE */
> >> + return true;
> >
> > So as of this patch except FUSE_DAX_NEVER return true and this will
> > change in later patches for FUSE_DAX_INODE? If that's the case, keep
> > it simple in this patch and change it later in the patch series.
> >
> > fuse_should_enable_dax()
> > {
> > if (dax_mode == FUSE_DAX_NEVER)
> > return false;
> > return true;
> > }
> >
> >> }
> >>
> >> void fuse_dax_inode_init(struct inode *inode)
> >> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> >> index 319596df5dc6..5abf9749923f 100644
> >> --- a/fs/fuse/fuse_i.h
> >> +++ b/fs/fuse/fuse_i.h
> >> @@ -480,6 +480,12 @@ struct fuse_dev {
> >> struct list_head entry;
> >> };
> >>
> >> +enum fuse_dax_mode {
> >> + FUSE_DAX_INODE,
> >> + FUSE_DAX_ALWAYS,
> >> + FUSE_DAX_NEVER,
> >> +};
> >> +
> >> struct fuse_fs_context {
> >> int fd;
> >> struct file *file;
> >> @@ -497,7 +503,7 @@ struct fuse_fs_context {
> >> bool no_control:1;
> >> bool no_force_umount:1;
> >> bool legacy_opts_show:1;
> >> - bool dax:1;
> >> + enum fuse_dax_mode dax_mode;
> >> unsigned int max_read;
> >> unsigned int blksize;
> >> const char *subtype;
> >> @@ -802,6 +808,9 @@ struct fuse_conn {
> >> struct list_head devices;
> >>
> >> #ifdef CONFIG_FUSE_DAX
> >> + /* dax mode: FUSE_DAX_* (always, never or per-file) */
> >> + enum fuse_dax_mode dax_mode;
> >> +
> >> /* Dax specific conn data, non-NULL if DAX is enabled */
> >> struct fuse_conn_dax *dax;
> >> #endif
> >> @@ -1255,7 +1264,8 @@ ssize_t fuse_dax_read_iter(struct kiocb *iocb, struct iov_iter *to);
> >> ssize_t fuse_dax_write_iter(struct kiocb *iocb, struct iov_iter *from);
> >> int fuse_dax_mmap(struct file *file, struct vm_area_struct *vma);
> >> int fuse_dax_break_layouts(struct inode *inode, u64 dmap_start, u64 dmap_end);
> >> -int fuse_dax_conn_alloc(struct fuse_conn *fc, struct dax_device *dax_dev);
> >> +int fuse_dax_conn_alloc(struct fuse_conn *fc, enum fuse_dax_mode mode,
> >> + struct dax_device *dax_dev);
> >> void fuse_dax_conn_free(struct fuse_conn *fc);
> >> bool fuse_dax_inode_alloc(struct super_block *sb, struct fuse_inode *fi);
> >> void fuse_dax_inode_init(struct inode *inode);
> >> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> >> index 36cd03114b6d..b4b41683e97e 100644
> >> --- a/fs/fuse/inode.c
> >> +++ b/fs/fuse/inode.c
> >> @@ -742,8 +742,12 @@ static int fuse_show_options(struct seq_file *m, struct dentry *root)
> >> seq_printf(m, ",blksize=%lu", sb->s_blocksize);
> >> }
> >> #ifdef CONFIG_FUSE_DAX
> >> - if (fc->dax)
> >> - seq_puts(m, ",dax");
> >> + if (fc->dax_mode == FUSE_DAX_ALWAYS)
> >> + seq_puts(m, ",dax=always");
> >
> > So if somebody mounts with "-o dax" then kernel previous to this change
> > will show "dax" and kernel after this change will show "dax=always"?
>
> Yes. It's actually how per-file DAX on ext4/xfs behaves.
>
> >
> > How about not change the behavior. Keep a mode say FUSE_DAX_LEGACY which
> > will be set when user specifies "-o dax". Internally FUSE_DAX_LEGACY
> > and FUSE_DAX_ALWAYS will be same.
> >
> > if (fc->dax_mode == FUSE_DAX_LEGACY)
> > seq_puts(m, ",dax");
> >
>
>
>
>
> >
> >> + else if (fc->dax_mode == FUSE_DAX_NEVER)
> >> + seq_puts(m, ",dax=never");
> >> + else if (fc->dax_mode == FUSE_DAX_INODE)
> >> + seq_puts(m, ",dax=inode");
> >> #endif
> >>
> >> return 0;
> >> @@ -1493,7 +1497,7 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
> >> sb->s_subtype = ctx->subtype;
> >> ctx->subtype = NULL;
> >> if (IS_ENABLED(CONFIG_FUSE_DAX)) {
> >> - err = fuse_dax_conn_alloc(fc, ctx->dax_dev);
> >> + err = fuse_dax_conn_alloc(fc, ctx->dax_mode, ctx->dax_dev);
> >> if (err)
> >> goto err;
> >> }
> >> diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
> >> index 0ad89c6629d7..58cfbaeb4a7d 100644
> >> --- a/fs/fuse/virtio_fs.c
> >> +++ b/fs/fuse/virtio_fs.c
> >> @@ -88,12 +88,21 @@ struct virtio_fs_req_work {
> >> static int virtio_fs_enqueue_req(struct virtio_fs_vq *fsvq,
> >> struct fuse_req *req, bool in_flight);
> >>
> >> +static const struct constant_table dax_param_enums[] = {
> >> + {"inode", FUSE_DAX_INODE },
> >> + {"always", FUSE_DAX_ALWAYS },
> >> + {"never", FUSE_DAX_NEVER },
> >> + {}
> >> +};
> >> +
> >> enum {
> >> OPT_DAX,
> >> + OPT_DAX_ENUM,
> >> };
> >>
> >> static const struct fs_parameter_spec virtio_fs_parameters[] = {
> >> fsparam_flag("dax", OPT_DAX),
> >> + fsparam_enum("dax", OPT_DAX_ENUM, dax_param_enums),
> >> {}
> >> };
> >>
> >> @@ -110,7 +119,10 @@ static int virtio_fs_parse_param(struct fs_context *fsc,
> >>
> >> switch (opt) {
> >> case OPT_DAX:
> >> - ctx->dax = 1;
> >> + ctx->dax_mode = FUSE_DAX_ALWAYS;
> >> + break;
> >> + case OPT_DAX_ENUM:
> >> + ctx->dax_mode = result.uint_32;
> >> break;
> >> default:
> >> return -EINVAL;
> >> @@ -1326,7 +1338,7 @@ static int virtio_fs_fill_super(struct super_block *sb, struct fs_context *fsc)
> >>
> >> /* virtiofs allocates and installs its own fuse devices */
> >> ctx->fudptr = NULL;
> >> - if (ctx->dax) {
> >> + if (ctx->dax_mode != FUSE_DAX_NEVER) {
> >> if (!fs->dax_dev) {
> >> err = -EINVAL;
> >> pr_err("virtio-fs: dax can't be enabled as filesystem"
> >> --
> >> 2.27.0
> >>
>
> --
> Thanks,
> Jeffle
>
