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xfs: avoid COW fork extent lookups in writeback if the fork didn't change 

Used the per-fork sequence counter to avoid lookups in the writeback code
unless the COW fork actually changed.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Christoph Hellwig 2018-07-17 16:51:52 -07:00 committed by Darrick J. Wong
parent 745b3f76d1
commit e666aa37f4
3 changed files with 38 additions and 7 deletions
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38
fs/xfs/xfs_aops.c
View File

@ -29,6 +29,7 @@
struct xfs_writepage_ctx {
struct xfs_bmbt_irec imap;
unsigned int io_type;
unsigned int cow_seq;
struct xfs_ioend *ioend;
};
@ -310,6 +311,7 @@ xfs_map_blocks(
struct xfs_mount *mp = ip->i_mount;
ssize_t count = i_blocksize(inode);
xfs_fileoff_t offset_fsb = XFS_B_TO_FSBT(mp, offset), end_fsb;
xfs_fileoff_t cow_fsb = NULLFILEOFF;
struct xfs_bmbt_irec imap;
int whichfork = XFS_DATA_FORK;
struct xfs_iext_cursor icur;
@ -333,12 +335,23 @@ xfs_map_blocks(
* COW fork blocks can overlap data fork blocks even if the blocks
* aren't shared. COW I/O always takes precedent, so we must always
* check for overlap on reflink inodes unless the mapping is already a
* COW one.
* COW one, or the COW fork hasn't changed from the last time we looked
* at it.
*
* It's safe to check the COW fork if_seq here without the ILOCK because
* we've indirectly protected against concurrent updates: writeback has
* the page locked, which prevents concurrent invalidations by reflink
* and directio and prevents concurrent buffered writes to the same
* page. Changes to if_seq always happen under i_lock, which protects
* against concurrent updates and provides a memory barrier on the way
* out that ensures that we always see the current value.
*/
imap_valid = offset_fsb >= wpc->imap.br_startoff &&
offset_fsb < wpc->imap.br_startoff + wpc->imap.br_blockcount;
if (imap_valid &&
(!xfs_inode_has_cow_data(ip) || wpc->io_type == XFS_IO_COW))
(!xfs_inode_has_cow_data(ip) ||
wpc->io_type == XFS_IO_COW ||
wpc->cow_seq == ip->i_cowfp->if_seq))
return 0;
if (XFS_FORCED_SHUTDOWN(mp))
@ -364,8 +377,10 @@ xfs_map_blocks(
* it directly instead of looking up anything in the data fork.
*/
if (xfs_inode_has_cow_data(ip) &&
xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, &imap) &&
imap.br_startoff <= offset_fsb) {
xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, &imap))
cow_fsb = imap.br_startoff;
if (cow_fsb != NULLFILEOFF && cow_fsb <= offset_fsb) {
wpc->cow_seq = ip->i_cowfp->if_seq;
xfs_iunlock(ip, XFS_ILOCK_SHARED);
/*
* Truncate can race with writeback since writeback doesn't
@ -411,6 +426,16 @@ xfs_map_blocks(
imap.br_startblock = HOLESTARTBLOCK;
wpc->io_type = XFS_IO_HOLE;
} else {
/*
* Truncate to the next COW extent if there is one. This is the
* only opportunity to do this because we can skip COW fork
* lookups for the subsequent blocks in the mapping; however,
* the requirement to treat the COW range separately remains.
*/
if (cow_fsb != NULLFILEOFF &&
cow_fsb < imap.br_startoff + imap.br_blockcount)
imap.br_blockcount = cow_fsb - imap.br_startoff;
if (isnullstartblock(imap.br_startblock)) {
/* got a delalloc extent */
wpc->io_type = XFS_IO_DELALLOC;
@ -427,9 +452,12 @@ xfs_map_blocks(
trace_xfs_map_blocks_found(ip, offset, count, wpc->io_type, &imap);
return 0;
allocate_blocks:
error = xfs_iomap_write_allocate(ip, whichfork, offset, &imap);
error = xfs_iomap_write_allocate(ip, whichfork, offset, &imap,
&wpc->cow_seq);
if (error)
return error;
ASSERT(whichfork == XFS_COW_FORK || cow_fsb == NULLFILEOFF ||
imap.br_startoff + imap.br_blockcount <= cow_fsb);
wpc->imap = imap;
trace_xfs_map_blocks_alloc(ip, offset, count, wpc->io_type, &imap);
return 0;

5
fs/xfs/xfs_iomap.c
View File

@ -651,7 +651,8 @@ xfs_iomap_write_allocate(
xfs_inode_t *ip,
int whichfork,
xfs_off_t offset,
xfs_bmbt_irec_t *imap)
xfs_bmbt_irec_t *imap,
unsigned int *cow_seq)
{
xfs_mount_t *mp = ip->i_mount;
xfs_fileoff_t offset_fsb, last_block;
@ -766,6 +767,8 @@ xfs_iomap_write_allocate(
if (error)
goto error0;
if (whichfork == XFS_COW_FORK)
*cow_seq = XFS_IFORK_PTR(ip, whichfork)->if_seq;
xfs_iunlock(ip, XFS_ILOCK_EXCL);
}

2
fs/xfs/xfs_iomap.h
View File

@ -14,7 +14,7 @@ struct xfs_bmbt_irec;
int xfs_iomap_write_direct(struct xfs_inode *, xfs_off_t, size_t,
struct xfs_bmbt_irec *, int);
int xfs_iomap_write_allocate(struct xfs_inode *, int, xfs_off_t,
struct xfs_bmbt_irec *);
struct xfs_bmbt_irec *, unsigned int *);
int xfs_iomap_write_unwritten(struct xfs_inode *, xfs_off_t, xfs_off_t, bool);
void xfs_bmbt_to_iomap(struct xfs_inode *, struct iomap *,