Re: [PATCH 4/4] xfs: use separate btree cursor slab for each btree type

Dave Chinner
2021-09-26T00:47:25Z

On Thu, Sep 23, 2021 at 06:27:59PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
>
> Now that we have the infrastructure to track the max possible height of
> each btree type, we can create a separate slab zone for cursors of each
> type of btree. For smaller indices like the free space btrees, this
> means that we can pack more cursors into a slab page, improving slab
> utilization.
>
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
> fs/xfs/libxfs/xfs_btree.c | 12 ++++++------
> fs/xfs/libxfs/xfs_btree.h | 9 +--------
> fs/xfs/xfs_super.c | 33 ++++++++++++++++++++++++---------
> 3 files changed, 31 insertions(+), 23 deletions(-)
>
>
> diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
> index 120280c998f8..3131de9ae631 100644
> --- a/fs/xfs/libxfs/xfs_btree.c
> +++ b/fs/xfs/libxfs/xfs_btree.c
> @@ -26,7 +26,6 @@
> /*
> * Cursor allocation zone.
> */
> -kmem_zone_t *xfs_btree_cur_zone;
> struct xfs_btree_cur_zone xfs_btree_cur_zones[XFS_BTNUM_MAX] = {
> [XFS_BTNUM_BNO] = { .name = "xfs_alloc_btree_cur" },
> [XFS_BTNUM_INO] = { .name = "xfs_ialloc_btree_cur" },
> @@ -364,6 +363,7 @@ xfs_btree_del_cursor(
> struct xfs_btree_cur *cur, /* btree cursor */
> int error) /* del because of error */
> {
> + struct xfs_btree_cur_zone *bczone = &xfs_btree_cur_zones[cur->bc_btnum];
> int i; /* btree level */
>
> /*
> @@ -386,10 +386,10 @@ xfs_btree_del_cursor(
> kmem_free(cur->bc_ops);
> if (!(cur->bc_flags & XFS_BTREE_LONG_PTRS) && cur->bc_ag.pag)
> xfs_perag_put(cur->bc_ag.pag);
> - if (cur->bc_maxlevels > XFS_BTREE_CUR_ZONE_MAXLEVELS)
> + if (cur->bc_maxlevels > bczone->maxlevels)
> kmem_free(cur);
> else
> - kmem_cache_free(xfs_btree_cur_zone, cur);
> + kmem_cache_free(bczone->zone, cur);
> }
>
> /*
> @@ -5021,12 +5021,12 @@ xfs_btree_alloc_cursor(
> {
> struct xfs_btree_cur *cur;
> unsigned int maxlevels = xfs_btree_maxlevels(mp, btnum);
> + struct xfs_btree_cur_zone *bczone = &xfs_btree_cur_zones[btnum];
>
> - if (maxlevels > XFS_BTREE_CUR_ZONE_MAXLEVELS)
> + if (maxlevels > bczone->maxlevels)
> cur = kmem_zalloc(xfs_btree_cur_sizeof(maxlevels), KM_NOFS);
> else
> - cur = kmem_cache_zalloc(xfs_btree_cur_zone,
> - GFP_NOFS | __GFP_NOFAIL);
> + cur = kmem_cache_zalloc(bczone->zone, GFP_NOFS | __GFP_NOFAIL);

When will maxlevels ever be greater than bczone->maxlevels? Isn't
the bczone->maxlevels case always supposed to be the tallest
possible height for that btree?

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com