On Thu, 2023-01-19 at 09:44 +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
Ok, makes sense
Reviewed-by: Allison Henderson <allison.henderson@xxxxxxxxxx>
> ---
> 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 5b8401038bab..c8d837d8876f 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);
