Re: [PATCH v5 2/3] xfs: introduce in-core global counter of allocbt blocks

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Apr 28, 2021 at 12:57:09PM -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>
> Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
> Reviewed-by: Allison Henderson <allison.henderson@oracle.com>

Looks better, let's see what happens when I throw it at fstests...
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  fs/xfs/libxfs/xfs_alloc.c       | 14 ++++++++++++++
>  fs/xfs/libxfs/xfs_alloc_btree.c |  2 ++
>  fs/xfs/xfs_mount.h              |  6 ++++++
>  3 files changed, 22 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index aaa19101bb2a..b6a082348e46 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;
> +	int			allocbt_blks;
>  
>  	trace_xfs_alloc_read_agf(mp, agno);
>  
> @@ -3066,6 +3067,19 @@ 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 in-core allocbt counter. Filter out the rmapbt
> +		 * subset of the btreeblks counter because the rmapbt is managed
> +		 * by perag reservation. Subtract one for the rmapbt root block
> +		 * because the rmap counter includes it while the btreeblks
> +		 * counter only tracks non-root blocks.
> +		 */
> +		allocbt_blks = pag->pagf_btreeblks;
> +		if (xfs_sb_version_hasrmapbt(&mp->m_sb))
> +			allocbt_blks -= be32_to_cpu(agf->agf_rmap_blocks) - 1;
> +		if (allocbt_blks > 0)
> +			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
>