Re: [PATCH v4 2/3] xfs: introduce in-core global counter of allocbt blocks

Darrick J. Wong
2021-04-28T04:15:12Z

On Fri, Apr 23, 2021 at 09:10:49AM -0400, Brian Foster wrote:
> Introduce an in-core counter to track the sum of all allocbt blocks
> used by the filesystem. This value is currently tracked per-ag via
> the ->agf_btreeblks field in the AGF, which also happens to include
> rmapbt blocks. A global, in-core count of allocbt blocks is required
> to identify the subset of global ->m_fdblocks that consists of
> unavailable blocks currently used for allocation btrees. To support
> this calculation at block reservation time, construct a similar
> global counter for allocbt blocks, populate it on first read of each
> AGF and update it as allocbt blocks are used and released.
>
> Signed-off-by: Brian Foster <bfoster@redhat.com>
> ---
> fs/xfs/libxfs/xfs_alloc.c | 12 ++++++++++++
> fs/xfs/libxfs/xfs_alloc_btree.c | 2 ++
> fs/xfs/xfs_mount.h | 6 ++++++
> 3 files changed, 20 insertions(+)
>
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index aaa19101bb2a..144e2d68245c 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -3036,6 +3036,7 @@ xfs_alloc_read_agf(
> struct xfs_agf *agf; /* ag freelist header */
> struct xfs_perag *pag; /* per allocation group data */
> int error;
> + uint32_t allocbt_blks;
>
> trace_xfs_alloc_read_agf(mp, agno);
>
> @@ -3066,6 +3067,17 @@ xfs_alloc_read_agf(
> pag->pagf_refcount_level = be32_to_cpu(agf->agf_refcount_level);
> pag->pagf_init = 1;
> pag->pagf_agflreset = xfs_agfl_needs_reset(mp, agf);
> +
> + /*
> + * Update the global in-core allocbt block counter. Filter
> + * rmapbt blocks from the on-disk counter because those are
> + * managed by perag reservation.
> + */
> + if (pag->pagf_btreeblks > be32_to_cpu(agf->agf_rmap_blocks)) {

As pointed out elsewhere in the thread, agf_rmap_blocks counts the total
number of blocks in the rmapbt (whereas agf_btreeblks counts the number
of non-root blocks in all three free space btrees). Does this need a
change?

int delta = (int)pag->pagf_btreeblks - (be32_to_cpu(...) - 1);
if (delta > 0)
atomic64_add(delta, &mp->m_allocbt_blks);

--D

> + allocbt_blks = pag->pagf_btreeblks -
> + be32_to_cpu(agf->agf_rmap_blocks);
> + atomic64_add(allocbt_blks, &mp->m_allocbt_blks);
> + }
> }
> #ifdef DEBUG
> else if (!XFS_FORCED_SHUTDOWN(mp)) {
> diff --git a/fs/xfs/libxfs/xfs_alloc_btree.c b/fs/xfs/libxfs/xfs_alloc_btree.c
> index 8e01231b308e..9f5a45f7baed 100644
> --- a/fs/xfs/libxfs/xfs_alloc_btree.c
> +++ b/fs/xfs/libxfs/xfs_alloc_btree.c
> @@ -71,6 +71,7 @@ xfs_allocbt_alloc_block(
> return 0;
> }
>
> + atomic64_inc(&cur->bc_mp->m_allocbt_blks);
> xfs_extent_busy_reuse(cur->bc_mp, cur->bc_ag.agno, bno, 1, false);
>
> xfs_trans_agbtree_delta(cur->bc_tp, 1);
> @@ -95,6 +96,7 @@ xfs_allocbt_free_block(
> if (error)
> return error;
>
> + atomic64_dec(&cur->bc_mp->m_allocbt_blks);
> xfs_extent_busy_insert(cur->bc_tp, be32_to_cpu(agf->agf_seqno), bno, 1,
> XFS_EXTENT_BUSY_SKIP_DISCARD);
> xfs_trans_agbtree_delta(cur->bc_tp, -1);
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index 81829d19596e..bb67274ee23f 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -170,6 +170,12 @@ typedef struct xfs_mount {
> * extents or anything related to the rt device.
> */
> struct percpu_counter m_delalloc_blks;
> + /*
> + * Global count of allocation btree blocks in use across all AGs. Only
> + * used when perag reservation is enabled. Helps prevent block
> + * reservation from attempting to reserve allocation btree blocks.
> + */
> + atomic64_t m_allocbt_blks;
>
> struct radix_tree_root m_perag_tree; /* per-ag accounting info */
> spinlock_t m_perag_lock; /* lock for m_perag_tree */
> --
> 2.26.3
>