[RFC v2 PATCH 09/10] xfs: support no block reservation transaction mode

Brian Foster
2016-04-12T16:43:00Z

The block device reservation mechanism is tied into the transaction
reservation mechanism and assumes the worst case scenario of a 1-1
mapping between filesystem blocks and dm blocks. This might be overkill
for certain codepaths that have enough context to not require a
worst-case reservation.

Define an optional transaction flag to disable block reservation on a
per-transaction basis. This allows any particular operation to open code
a block device reservation and potentially use a more optimal
reservation value.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
fs/xfs/libxfs/xfs_shared.h | 2 ++
fs/xfs/xfs_trans.c | 10 ++++++----
2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_shared.h b/fs/xfs/libxfs/xfs_shared.h
index 81ac870..ba79373 100644
--- a/fs/xfs/libxfs/xfs_shared.h
+++ b/fs/xfs/libxfs/xfs_shared.h
@@ -183,6 +183,8 @@ int xfs_log_calc_minimum_size(struct xfs_mount *);
#define XFS_TRANS_RESERVE 0x20 /* OK to use reserved data blocks */
#define XFS_TRANS_FREEZE_PROT 0x40 /* Transaction has elevated writer
count in superblock */
+#define XFS_TRANS_NOBLKRES 0x100 /* do not attempt blkdev reservation */
+
/*
* Field values for xfs_trans_mod_sb.
*/
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 26e6288..343e435 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -174,11 +174,13 @@ xfs_trans_reserve(
uint rtextents)
{
int error = 0;
- int flags = 0;
+ int flags = XFS_BLK_RES;
struct xfs_mount *mp = tp->t_mountp;

if (tp->t_flags & XFS_TRANS_RESERVE)
flags |= XFS_FDBLOCKS_RSVD;
+ if (tp->t_flags & XFS_TRANS_NOBLKRES)
+ flags &= ~XFS_BLK_RES;

/* Mark this thread as being in a transaction */
current_set_flags_nested(&tp->t_pflags, PF_FSTRANS);
@@ -189,13 +191,13 @@ xfs_trans_reserve(
* fail if the count would go below zero.
*/
if (blocks > 0) {
- error = xfs_mod_fdblocks(mp, -((int64_t)blocks), flags);
+ error = __xfs_mod_fdblocks(mp, -((int64_t)blocks), flags);
if (error != 0) {
current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
return -ENOSPC;
}
tp->t_blk_res += blocks;
- if (mp->m_thin_res)
+ if (mp->m_thin_res && (flags & XFS_BLK_RES))
tp->t_blk_thin_res += xfs_fsb_res(mp, blocks, false);
}

@@ -266,7 +268,7 @@ undo_log:

undo_blocks:
if (blocks > 0) {
- xfs_mod_fdblocks(tp->t_mountp, -((int64_t)blocks), flags);
+ __xfs_mod_fdblocks(tp->t_mountp, -((int64_t)blocks), flags);
tp->t_blk_res = 0;
if (tp->t_blk_thin_res)
tp->t_blk_thin_res = 0;
--
2.4.11