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

Brian Foster
2021-04-28T15:02:14Z

On Tue, Apr 27, 2021 at 09:15:09PM -0700, Darrick J. Wong wrote:
> 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);
>

Hm yes, this makes more sense. Will fix and update the comment..

Brian

> --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
> >
>