On Thu, Nov 25, 2021 at 03:05:27PM +0800, Jeffle Xu wrote:
> DAX may be limited in some specific situation. When the number of usable
> DAX windows is under watermark, the recalim routine will be triggered to
> reclaim some DAX windows. It may have a negative impact on the
> performance, since some processes may need to wait for DAX windows to be
> recalimed and reused then. To mitigate the performance degradation, the
> overall DAX window need to be expanded larger.
>
> However, simply expanding the DAX window may not be a good deal in some
> scenario. To maintain one DAX window chunk (i.e., 2MB in size), 32KB
> (512 * 64 bytes) memory footprint will be consumed for page descriptors
> inside guest, which is greater than the memory footprint if it uses
> guest page cache when DAX disabled. Thus it'd better disable DAX for
> those files smaller than 32KB, to reduce the demand for DAX window and
> thus avoid the unworthy memory overhead.
>
> Per inode DAX feature is introduced to address this issue, by offering a
> finer grained control for dax to users, trying to achieve a balance
> between performance and memory overhead.
>
> The FUSE_ATTR_DAX flag in FUSE_LOOKUP reply is used to indicate whether
> DAX should be enabled or not for corresponding file. Currently the state
> whether DAX is enabled or not for the file is initialized only when
> inode is instantiated.
>
> Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
Reviwed-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
Vivek
> ---
> fs/fuse/dax.c | 12 ++++++++----
> fs/fuse/file.c | 4 ++--
> fs/fuse/fuse_i.h | 4 ++--
> fs/fuse/inode.c | 2 +-
> 4 files changed, 13 insertions(+), 9 deletions(-)
>
> diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
> index b9a031a82934..1550c3624414 100644
> --- a/fs/fuse/dax.c
> +++ b/fs/fuse/dax.c
> @@ -1332,7 +1332,7 @@ static const struct address_space_operations fuse_dax_file_aops = {
> .invalidatepage = noop_invalidatepage,
> };
>
> -static bool fuse_should_enable_dax(struct inode *inode)
> +static bool fuse_should_enable_dax(struct inode *inode, unsigned int flags)
> {
> struct fuse_conn *fc = get_fuse_conn(inode);
> enum fuse_dax_mode dax_mode = fc->dax_mode;
> @@ -1347,12 +1347,16 @@ static bool fuse_should_enable_dax(struct inode *inode)
> if (!fc->dax)
> return false;
>
> - return true;
> + if (dax_mode == FUSE_DAX_ALWAYS)
> + return true;
> +
> + /* dax_mode is FUSE_DAX_INODE* */
> + return flags & FUSE_ATTR_DAX;
> }
>
> -void fuse_dax_inode_init(struct inode *inode)
> +void fuse_dax_inode_init(struct inode *inode, unsigned int flags)
> {
> - if (!fuse_should_enable_dax(inode))
> + if (!fuse_should_enable_dax(inode, flags))
> return;
>
> inode->i_flags |= S_DAX;
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 9d6c5f6361f7..90067584e103 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -3169,7 +3169,7 @@ static const struct address_space_operations fuse_file_aops = {
> .write_end = fuse_write_end,
> };
>
> -void fuse_init_file_inode(struct inode *inode)
> +void fuse_init_file_inode(struct inode *inode, unsigned int flags)
> {
> struct fuse_inode *fi = get_fuse_inode(inode);
>
> @@ -3183,5 +3183,5 @@ void fuse_init_file_inode(struct inode *inode)
> fi->writepages = RB_ROOT;
>
> if (IS_ENABLED(CONFIG_FUSE_DAX))
> - fuse_dax_inode_init(inode);
> + fuse_dax_inode_init(inode, flags);
> }
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index 19ded93cfc49..f03ea7cb74b0 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -1022,7 +1022,7 @@ int fuse_notify_poll_wakeup(struct fuse_conn *fc,
> /**
> * Initialize file operations on a regular file
> */
> -void fuse_init_file_inode(struct inode *inode);
> +void fuse_init_file_inode(struct inode *inode, unsigned int flags);
>
> /**
> * Initialize inode operations on regular files and special files
> @@ -1288,7 +1288,7 @@ 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);
> +void fuse_dax_inode_init(struct inode *inode, unsigned int flags);
> void fuse_dax_inode_cleanup(struct inode *inode);
> bool fuse_dax_check_alignment(struct fuse_conn *fc, unsigned int map_alignment);
> void fuse_dax_cancel_work(struct fuse_conn *fc);
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 4a41e6a73f3f..0669e41a9645 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -313,7 +313,7 @@ static void fuse_init_inode(struct inode *inode, struct fuse_attr *attr)
> inode->i_ctime.tv_nsec = attr->ctimensec;
> if (S_ISREG(inode->i_mode)) {
> fuse_init_common(inode);
> - fuse_init_file_inode(inode);
> + fuse_init_file_inode(inode, attr->flags);
> } else if (S_ISDIR(inode->i_mode))
> fuse_init_dir(inode);
> else if (S_ISLNK(inode->i_mode))
> --
> 2.27.0
>
