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    Subject[PATCH v12 05/20] vfs,ext2: Introduce IS_DAX(inode)
    Date
    Use an inode flag to tag inodes which should avoid using the page cache.
    Convert ext2 to use it instead of mapping_is_xip(). Prevent I/Os to
    files tagged with the DAX flag from falling back to buffered I/O.

    Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
    Reviewed-by: Jan Kara <jack@suse.cz>
    Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    ---
    fs/ext2/inode.c | 9 ++++++---
    fs/ext2/xip.h | 2 --
    include/linux/fs.h | 6 ++++++
    mm/filemap.c | 19 ++++++++++++-------
    4 files changed, 24 insertions(+), 12 deletions(-)

    diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
    index 36d35c3..0cb0448 100644
    --- a/fs/ext2/inode.c
    +++ b/fs/ext2/inode.c
    @@ -731,7 +731,7 @@ static int ext2_get_blocks(struct inode *inode,
    goto cleanup;
    }

    - if (ext2_use_xip(inode->i_sb)) {
    + if (IS_DAX(inode)) {
    /*
    * we need to clear the block
    */
    @@ -1201,7 +1201,7 @@ static int ext2_setsize(struct inode *inode, loff_t newsize)

    inode_dio_wait(inode);

    - if (mapping_is_xip(inode->i_mapping))
    + if (IS_DAX(inode))
    error = xip_truncate_page(inode->i_mapping, newsize);
    else if (test_opt(inode->i_sb, NOBH))
    error = nobh_truncate_page(inode->i_mapping,
    @@ -1273,7 +1273,8 @@ void ext2_set_inode_flags(struct inode *inode)
    {
    unsigned int flags = EXT2_I(inode)->i_flags;

    - inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
    + inode->i_flags &= ~(S_SYNC | S_APPEND | S_IMMUTABLE | S_NOATIME |
    + S_DIRSYNC | S_DAX);
    if (flags & EXT2_SYNC_FL)
    inode->i_flags |= S_SYNC;
    if (flags & EXT2_APPEND_FL)
    @@ -1284,6 +1285,8 @@ void ext2_set_inode_flags(struct inode *inode)
    inode->i_flags |= S_NOATIME;
    if (flags & EXT2_DIRSYNC_FL)
    inode->i_flags |= S_DIRSYNC;
    + if (test_opt(inode->i_sb, XIP))
    + inode->i_flags |= S_DAX;
    }

    /* Propagate flags from i_flags to EXT2_I(inode)->i_flags */
    diff --git a/fs/ext2/xip.h b/fs/ext2/xip.h
    index 18b34d2..29be737 100644
    --- a/fs/ext2/xip.h
    +++ b/fs/ext2/xip.h
    @@ -16,9 +16,7 @@ static inline int ext2_use_xip (struct super_block *sb)
    }
    int ext2_get_xip_mem(struct address_space *, pgoff_t, int,
    void **, unsigned long *);
    -#define mapping_is_xip(map) unlikely(map->a_ops->get_xip_mem)
    #else
    -#define mapping_is_xip(map) 0
    #define ext2_xip_verify_sb(sb) do { } while (0)
    #define ext2_use_xip(sb) 0
    #define ext2_clear_xip_target(inode, chain) 0
    diff --git a/include/linux/fs.h b/include/linux/fs.h
    index a957d43..ff0acb2 100644
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -1587,6 +1587,11 @@ struct super_operations {
    #define S_IMA 1024 /* Inode has an associated IMA struct */
    #define S_AUTOMOUNT 2048 /* Automount/referral quasi-directory */
    #define S_NOSEC 4096 /* no suid or xattr security attributes */
    +#ifdef CONFIG_FS_XIP
    +#define S_DAX 8192 /* Direct Access, avoiding the page cache */
    +#else
    +#define S_DAX 0 /* Make all the DAX code disappear */
    +#endif

    /*
    * Note that nosuid etc flags are inode-specific: setting some file-system
    @@ -1624,6 +1629,7 @@ struct super_operations {
    #define IS_IMA(inode) ((inode)->i_flags & S_IMA)
    #define IS_AUTOMOUNT(inode) ((inode)->i_flags & S_AUTOMOUNT)
    #define IS_NOSEC(inode) ((inode)->i_flags & S_NOSEC)
    +#define IS_DAX(inode) ((inode)->i_flags & S_DAX)

    /*
    * Inode state bits. Protected by inode->i_lock
    diff --git a/mm/filemap.c b/mm/filemap.c
    index 14b4642..2b13a4a 100644
    --- a/mm/filemap.c
    +++ b/mm/filemap.c
    @@ -1727,9 +1727,11 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
    * we've already read everything we wanted to, or if
    * there was a short read because we hit EOF, go ahead
    * and return. Otherwise fallthrough to buffered io for
    - * the rest of the read.
    + * the rest of the read. Buffered reads will not work for
    + * DAX files, so don't bother trying.
    */
    - if (retval < 0 || !iov_iter_count(iter) || *ppos >= size) {
    + if (retval < 0 || !iov_iter_count(iter) || *ppos >= size ||
    + IS_DAX(inode)) {
    file_accessed(file);
    goto out;
    }
    @@ -2593,13 +2595,16 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
    loff_t endbyte;

    written = generic_file_direct_write(iocb, from, pos);
    - if (written < 0 || written == count)
    - goto out;
    -
    /*
    - * direct-io write to a hole: fall through to buffered I/O
    - * for completing the rest of the request.
    + * If the write stopped short of completing, fall back to
    + * buffered writes. Some filesystems do this for writes to
    + * holes, for example. For DAX files, a buffered write will
    + * not succeed (even if it did, DAX does not handle dirty
    + * page-cache pages correctly).
    */
    + if (written < 0 || written == count || IS_DAX(inode))
    + goto out;
    +
    pos += written;
    count -= written;

    --
    2.1.1


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