Re: [PATCH 3/6] xfs: add DAX file operations support

Jan Kara
2015-03-04T16:18:59Z

On Wed 04-03-15 10:30:24, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Add the initial support for DAX file operations to XFS. This
> includes the necessary block allocation and mmap page fault hooks
> for DAX to function.
>
> Note that the current block allocation code abuses the mapping
> buffer head to provide a completion callback for unwritten extent
> allocation when DAX is clearing blocks. The DAX interface needs to
> be changed to provide a callback similar to get_blocks for this
> callback.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_aops.c | 72 ++++++++++++++++++++++++++++++++++--
> fs/xfs/xfs_aops.h | 7 +++-
> fs/xfs/xfs_file.c | 108 ++++++++++++++++++++++++++++++++++++++++++++----------
> fs/xfs/xfs_iops.c | 4 ++
> fs/xfs/xfs_iops.h | 6 +++
> 5 files changed, 173 insertions(+), 24 deletions(-)
>
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 3a9b7a1..22cb03a 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -1233,13 +1233,63 @@ xfs_vm_releasepage(
> return try_to_free_buffers(page);
> }
>
> +/*
> + * For DAX we need a mapping buffer callback for unwritten extent conversion
> + * when page faults allocation blocks and then zero them.
> + */
> +#ifdef CONFIG_FS_DAX
> +static struct xfs_ioend *
> +xfs_dax_alloc_ioend(
> + struct inode *inode,
> + xfs_off_t offset,
> + ssize_t size)
> +{
> + struct xfs_ioend *ioend;
> +
> + ASSERT(IS_DAX(inode));
> + ioend = xfs_alloc_ioend(inode, XFS_IO_UNWRITTEN);
> + ioend->io_offset = offset;
> + ioend->io_size = size;
> + return ioend;
> +}
> +
> +void
> +xfs_get_blocks_dax_complete(
> + struct buffer_head *bh,
> + int uptodate)
> +{
> + struct xfs_ioend *ioend = bh->b_private;
> + struct xfs_inode *ip = XFS_I(ioend->io_inode);
> + int error;
> +
> + ASSERT(IS_DAX(ioend->io_inode));
> +
> + /* if there was an error zeroing, then don't convert it */
> + if (!uptodate)
> + goto out_free;
> +
> + error = xfs_iomap_write_unwritten(ip, ioend->io_offset, ioend->io_size);
> + if (error)
> + xfs_warn(ip->i_mount,
> +"%s: conversion failed, ino 0x%llx, offset 0x%llx, len 0x%lx, error %d\n",
> + __func__, ip->i_ino, ioend->io_offset,
> + ioend->io_size, error);
> +out_free:
> + mempool_free(ioend, xfs_ioend_pool);
> +
> +}
> +#else
> +#define xfs_dax_alloc_ioend(i,o,s) NULL
> +#endif
> +
> STATIC int
> __xfs_get_blocks(
> struct inode *inode,
> sector_t iblock,
> struct buffer_head *bh_result,
> int create,
> - int direct)
> + bool direct,
> + bool clear)
> {
> struct xfs_inode *ip = XFS_I(inode);
> struct xfs_mount *mp = ip->i_mount;
> @@ -1304,6 +1354,7 @@ __xfs_get_blocks(
> if (error)
> return error;
> new = 1;
> +
> } else {
> /*
> * Delalloc reservations do not require a transaction,
> @@ -1340,7 +1391,10 @@ __xfs_get_blocks(
> if (create || !ISUNWRITTEN(&imap))
> xfs_map_buffer(inode, bh_result, &imap, offset);
> if (create && ISUNWRITTEN(&imap)) {
> - if (direct) {
> + if (clear) {
> + bh_result->b_private = xfs_dax_alloc_ioend(
> + inode, offset, size);
> + } else if (direct) {
> bh_result->b_private = inode;
> set_buffer_defer_completion(bh_result);
> }
> @@ -1425,7 +1479,7 @@ xfs_get_blocks(
> struct buffer_head *bh_result,
> int create)
> {
> - return __xfs_get_blocks(inode, iblock, bh_result, create, 0);
> + return __xfs_get_blocks(inode, iblock, bh_result, create, false, false);
> }
>
> STATIC int
> @@ -1435,7 +1489,17 @@ xfs_get_blocks_direct(
> struct buffer_head *bh_result,
> int create)
> {
> - return __xfs_get_blocks(inode, iblock, bh_result, create, 1);
> + return __xfs_get_blocks(inode, iblock, bh_result, create, true, false);
> +}
> +
> +int
> +xfs_get_blocks_dax(
> + struct inode *inode,
> + sector_t iblock,
> + struct buffer_head *bh_result,
> + int create)
> +{
> + return __xfs_get_blocks(inode, iblock, bh_result, create, true, true);
> }
>
> /*
> diff --git a/fs/xfs/xfs_aops.h b/fs/xfs/xfs_aops.h
> index ac644e0..7c6fb3f 100644
> --- a/fs/xfs/xfs_aops.h
> +++ b/fs/xfs/xfs_aops.h
> @@ -53,7 +53,12 @@ typedef struct xfs_ioend {
> } xfs_ioend_t;
>
> extern const struct address_space_operations xfs_address_space_operations;
> -extern int xfs_get_blocks(struct inode *, sector_t, struct buffer_head *, int);
> +
> +int xfs_get_blocks(struct inode *inode, sector_t offset,
> + struct buffer_head *map_bh, int create);
> +int xfs_get_blocks_dax(struct inode *inode, sector_t offset,
> + struct buffer_head *map_bh, int create);
> +void xfs_get_blocks_dax_complete(struct buffer_head *bh, int uptodate);
>
> extern void xfs_count_page_state(struct page *, int *, int *);
>
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index bc0008f..4bfcba0 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -654,7 +654,7 @@ xfs_file_dio_aio_write(
> mp->m_rtdev_targp : mp->m_ddev_targp;
>
> /* DIO must be aligned to device logical sector size */
> - if ((pos | count) & target->bt_logical_sectormask)
> + if (!IS_DAX(inode) && (pos | count) & target->bt_logical_sectormask)
> return -EINVAL;
>
> /* "unaligned" here means not aligned to a filesystem block */
> @@ -724,8 +724,11 @@ xfs_file_dio_aio_write(
> out:
> xfs_rw_iunlock(ip, iolock);
>
> - /* No fallback to buffered IO on errors for XFS. */
> - ASSERT(ret < 0 || ret == count);
> + /*
> + * No fallback to buffered IO on errors for XFS. DAX can result in
> + * partial writes, but direct IO will either complete fully or fail.
> + */
> + ASSERT(ret < 0 || ret == count || IS_DAX(VFS_I(ip)));
> return ret;
> }
>
> @@ -810,7 +813,7 @@ xfs_file_write_iter(
> if (XFS_FORCED_SHUTDOWN(ip->i_mount))
> return -EIO;
>
> - if (unlikely(file->f_flags & O_DIRECT))
> + if ((file->f_flags & O_DIRECT) || IS_DAX(inode))
> ret = xfs_file_dio_aio_write(iocb, from);
> else
> ret = xfs_file_buffered_aio_write(iocb, from);
> @@ -1031,17 +1034,6 @@ xfs_file_readdir(
> return xfs_readdir(ip, ctx, bufsize);
> }
>
> -STATIC int
> -xfs_file_mmap(
> - struct file *filp,
> - struct vm_area_struct *vma)
> -{
> - vma->vm_ops = &xfs_file_vm_ops;
> -
> - file_accessed(filp);
> - return 0;
> -}
> -
> /*
> * This type is designed to indicate the type of offset we would like
> * to search from page cache for xfs_seek_hole_data().
> @@ -1466,6 +1458,71 @@ xfs_filemap_page_mkwrite(
> return error;
> }
>
> +static const struct vm_operations_struct xfs_file_vm_ops = {
> + .fault = xfs_filemap_fault,
> + .map_pages = filemap_map_pages,
> + .page_mkwrite = xfs_filemap_page_mkwrite,
> +};
> +
> +#ifdef CONFIG_FS_DAX
> +static int
> +xfs_filemap_dax_fault(
> + struct vm_area_struct *vma,
> + struct vm_fault *vmf)
> +{
> + struct xfs_inode *ip = XFS_I(vma->vm_file->f_mapping->host);
> + int error;
> +
> + trace_xfs_filemap_fault(ip);
> +
> + xfs_ilock(ip, XFS_MMAPLOCK_SHARED);
> + error = dax_fault(vma, vmf, xfs_get_blocks_dax,
> + xfs_get_blocks_dax_complete);
> + xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
> +
> + return error;
> +}
> +
> +static int
> +xfs_filemap_dax_page_mkwrite(
> + struct vm_area_struct *vma,
> + struct vm_fault *vmf)
> +{
> + struct xfs_inode *ip = XFS_I(vma->vm_file->f_mapping->host);
> + int error;
> +
> + trace_xfs_filemap_page_mkwrite(ip);
> +
> + xfs_ilock(ip, XFS_MMAPLOCK_SHARED);
So I think the lock ordering of XFS_MMAPLOCK and freezing protection is
suspicious (and actually so is for normal write faults as I'm looking -
didn't realize that when I was first reading your MMAPLOCK patches).
Because you take XFS_MMAPLOCK outside of freeze protection however usually
we want freeze protection to be the outermost lock - in particular in
xfs_file_fallocate() you take XFS_MMAPLOCK inside freeze protection I
think.

So you'll need to do what ext4 needs to do - take freeze protection, take
fs specific locks, and then call do_dax_fault(). Matthew has a patch to
actually export do_dax_fault (as __dax_fault()) for filesystems.

Similarly for xfs_filemap_page_mkwrite() you need to use
__block_page_mkwrite() as a callback (similarly as ext4 does) and do freeze
protection early by hand.

Honza

> + error = dax_mkwrite(vma, vmf, xfs_get_blocks_dax,
> + xfs_get_blocks_dax_complete);
> + xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
> +
> + return error;
> +}
> +
> +static const struct vm_operations_struct xfs_file_dax_vm_ops = {
> + .fault = xfs_filemap_dax_fault,
> + .page_mkwrite = xfs_filemap_dax_page_mkwrite,
> +};
> +#else
> +#define xfs_file_dax_vm_ops xfs_file_vm_ops
> +#endif /* CONFIG_FS_DAX */
> +
> +STATIC int
> +xfs_file_mmap(
> + struct file *filp,
> + struct vm_area_struct *vma)
> +{
> + file_accessed(filp);
> + if (IS_DAX(file_inode(filp))) {
> + vma->vm_ops = &xfs_file_dax_vm_ops;
> + vma->vm_flags |= VM_MIXEDMAP;
> + } else
> + vma->vm_ops = &xfs_file_vm_ops;
> + return 0;
> +}
> +
> const struct file_operations xfs_file_operations = {
> .llseek = xfs_file_llseek,
> .read = new_sync_read,
> @@ -1497,8 +1554,21 @@ const struct file_operations xfs_dir_file_operations = {
> .fsync = xfs_dir_fsync,
> };
>
> -static const struct vm_operations_struct xfs_file_vm_ops = {
> - .fault = xfs_filemap_fault,
> - .map_pages = filemap_map_pages,
> - .page_mkwrite = xfs_filemap_page_mkwrite,
> +#ifdef CONFIG_FS_DAX
> +const struct file_operations xfs_file_dax_operations = {
> + .llseek = xfs_file_llseek,
> + .read = new_sync_read,
> + .write = new_sync_write,
> + .read_iter = xfs_file_read_iter,
> + .write_iter = xfs_file_write_iter,
> + .unlocked_ioctl = xfs_file_ioctl,
> +#ifdef CONFIG_COMPAT
> + .compat_ioctl = xfs_file_compat_ioctl,
> +#endif
> + .mmap = xfs_file_mmap,
> + .open = xfs_file_open,
> + .release = xfs_file_release,
> + .fsync = xfs_file_fsync,
> + .fallocate = xfs_file_fallocate,
> };
> +#endif /* CONFIG_FS_DAX */
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 8b9e688..9f38142 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1264,6 +1264,10 @@ xfs_setup_inode(
> case S_IFREG:
> inode->i_op = &xfs_inode_operations;
> inode->i_fop = &xfs_file_operations;
> + if (IS_DAX(inode))
> + inode->i_fop = &xfs_file_dax_operations;
> + else
> + inode->i_fop = &xfs_file_operations;
> inode->i_mapping->a_ops = &xfs_address_space_operations;
> break;
> case S_IFDIR:
> diff --git a/fs/xfs/xfs_iops.h b/fs/xfs/xfs_iops.h
> index a0f84ab..c08983e 100644
> --- a/fs/xfs/xfs_iops.h
> +++ b/fs/xfs/xfs_iops.h
> @@ -23,6 +23,12 @@ struct xfs_inode;
> extern const struct file_operations xfs_file_operations;
> extern const struct file_operations xfs_dir_file_operations;
>
> +#ifdef CONFIG_FS_DAX
> +extern const struct file_operations xfs_file_dax_operations;
> +#else
> +#define xfs_file_dax_operations xfs_file_operations
> +#endif
> +
> extern ssize_t xfs_vn_listxattr(struct dentry *, char *data, size_t size);
>
> /*
> --
> 2.0.0
>
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR