On Mon, Sep 17, 2018 at 10:53:51PM +0200, Christoph Hellwig wrote:
> For files with extent size hints we always allocate unwritten extents
> first and then convert them to real extents later to avoid exposing
> stale data outside the blocks actually written. But there is no
> reason we can't do unwritten extent allocations from delalloc blocks,
> in fact we already do that for COW operations.
>
> Note that this does not handle files on the RT subvolume (yet), as
> we removed code handling RT allocations from the delalloc path this
> would be a slightly bigger project, and it doesn't really help with
> simplifying the COW path either.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/xfs/xfs_iomap.c | 17 ++++-------------
> 1 file changed, 4 insertions(+), 13 deletions(-)
>
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index e12ff5e9a8ec..2d08ace09e25 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -533,7 +533,6 @@ xfs_file_iomap_begin_delay(
> xfs_fsblock_t prealloc_blocks = 0;
>
> ASSERT(!XFS_IS_REALTIME_INODE(ip));
> - ASSERT(!xfs_get_extsz_hint(ip));
>
> xfs_ilock(ip, XFS_ILOCK_EXCL);
>
> @@ -1035,7 +1034,7 @@ xfs_file_iomap_begin(
> return -EIO;
>
> if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && !(flags & IOMAP_DIRECT) &&
> - !IS_DAX(inode) && !xfs_get_extsz_hint(ip)) {
> + !IS_DAX(inode) && !XFS_IS_REALTIME_INODE(ip)) {
AFAICT this fails to honor the extent size hint for buffered writes:
# xfs_io -fc "truncate 1m" -c "extsize 32k" -c "pwrite 0 4k" -c "fiemap -v" /mnt/file
wrote 4096/4096 bytes at offset 0
4 KiB, 1 ops; 0.0001 sec (35.511 MiB/sec and 9090.9091 ops/sec)
/mnt/file:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..7]: 80..87 8 0x1
1: [8..2047]: hole 2040
... and with an unpatched kernel:
# xfs_io -fc "truncate 1m" -c "extsize 32k" -c "pwrite 0 4k" -c "fiemap -v" /mnt/file
wrote 4096/4096 bytes at offset 0
4 KiB, 1 ops; 0.0017 sec (2.283 MiB/sec and 584.4535 ops/sec)
/mnt/file:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..7]: 192..199 8 0x0
1: [8..63]: 200..255 56 0x801
2: [64..2047]: hole 1984
I'd guess this is due to the extent overlap check in
xfs_bmap_extsize_align(), but I haven't verified.
Brian
> /* Reserve delalloc blocks for regular writeback. */
> return xfs_file_iomap_begin_delay(inode, offset, length, flags,
> iomap);
> @@ -1088,17 +1087,9 @@ xfs_file_iomap_begin(
> * been done up front, so we don't need to do them here.
> */
> if (xfs_is_reflink_inode(ip)) {
> - if (flags & IOMAP_DIRECT) {
> - /* may drop and re-acquire the ilock */
> - error = xfs_reflink_allocate_cow(ip, &imap, &shared,
> - &lockmode);
> - if (error)
> - goto out_unlock;
> - } else {
> - error = xfs_reflink_reserve_cow(ip, &imap, &shared);
> - if (error)
> - goto out_unlock;
> - }
> + error = xfs_reflink_allocate_cow(ip, &imap, &shared, &lockmode);
> + if (error)
> + goto out_unlock;
>
> end_fsb = imap.br_startoff + imap.br_blockcount;
> length = XFS_FSB_TO_B(mp, end_fsb) - offset;
> --
> 2.18.0
>
