[PATCH 12/42] xfs: convert xfs_ialloc_next_ag() to an atomic

Dave Chinner
2023-02-09T22:26:37Z

This is currently a spinlock lock protected rotor which can be
implemented with a single atomic operation. Change it to be more
efficient and get rid of the m_agirotor_lock. Noticed while
converting the inode allocation AG selection loop to active perag
references.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
---
fs/xfs/libxfs/xfs_ialloc.c | 17 +----------------
fs/xfs/libxfs/xfs_sb.c | 3 ++-
fs/xfs/xfs_mount.h | 3 +--
fs/xfs/xfs_super.c | 1 -
4 files changed, 4 insertions(+), 20 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
index c8b31c06a95d..86b7adc355e6 100644
--- a/fs/xfs/libxfs/xfs_ialloc.c
+++ b/fs/xfs/libxfs/xfs_ialloc.c
@@ -1576,21 +1576,6 @@ xfs_dialloc_roll(
return error;
}

-static xfs_agnumber_t
-xfs_ialloc_next_ag(
- xfs_mount_t *mp)
-{
- xfs_agnumber_t agno;
-
- spin_lock(&mp->m_agirotor_lock);
- agno = mp->m_agirotor;
- if (++mp->m_agirotor >= mp->m_maxagi)
- mp->m_agirotor = 0;
- spin_unlock(&mp->m_agirotor_lock);
-
- return agno;
-}
-
static bool
xfs_dialloc_good_ag(
struct xfs_perag *pag,
@@ -1748,7 +1733,7 @@ xfs_dialloc(
* an AG has enough space for file creation.
*/
if (S_ISDIR(mode))
- start_agno = xfs_ialloc_next_ag(mp);
+ start_agno = atomic_inc_return(&mp->m_agirotor) % mp->m_maxagi;
else {
start_agno = XFS_INO_TO_AGNO(mp, parent);
if (start_agno >= mp->m_maxagi)
diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
index 1eeecf2eb2a7..99cc03a298e2 100644
--- a/fs/xfs/libxfs/xfs_sb.c
+++ b/fs/xfs/libxfs/xfs_sb.c
@@ -909,7 +909,8 @@ xfs_sb_mount_common(
struct xfs_mount *mp,
struct xfs_sb *sbp)
{
- mp->m_agfrotor = mp->m_agirotor = 0;
+ mp->m_agfrotor = 0;
+ atomic_set(&mp->m_agirotor, 0);
mp->m_maxagi = mp->m_sb.sb_agcount;
mp->m_blkbit_log = sbp->sb_blocklog + XFS_NBBYLOG;
mp->m_blkbb_log = sbp->sb_blocklog - BBSHIFT;
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 8aca2cc173ac..f3269c0626f0 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -210,8 +210,7 @@ typedef struct xfs_mount {
struct xfs_error_cfg m_error_cfg[XFS_ERR_CLASS_MAX][XFS_ERR_ERRNO_MAX];
struct xstats m_stats; /* per-fs stats */
xfs_agnumber_t m_agfrotor; /* last ag where space found */
- xfs_agnumber_t m_agirotor; /* last ag dir inode alloced */
- spinlock_t m_agirotor_lock;/* .. and lock protecting it */
+ atomic_t m_agirotor; /* last ag dir inode alloced */

/* Memory shrinker to throttle and reprioritize inodegc */
struct shrinker m_inodegc_shrinker;
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 0c4b73e9b29d..96375b5622fd 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1922,7 +1922,6 @@ static int xfs_init_fs_context(
return -ENOMEM;

spin_lock_init(&mp->m_sb_lock);
- spin_lock_init(&mp->m_agirotor_lock);
INIT_RADIX_TREE(&mp->m_perag_tree, GFP_ATOMIC);
spin_lock_init(&mp->m_perag_lock);
mutex_init(&mp->m_growlock);
--
2.39.0