Re: [PATCH 15/24] xfs: allow multiple reclaimers per AG

Darrick J. Wong
2020-05-22T23:10:13Z

On Fri, May 22, 2020 at 01:50:20PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Inode reclaim will still throttle direct reclaim on the per-ag
> reclaim locks. This is no longer necessary as reclaim can run
> non-blocking now. Hence we can remove these locks so that we don't
> arbitrarily block reclaimers just because there are more direct
> reclaimers than there are AGs.
>
> This can result in multiple reclaimers working on the same range of
> an AG, but this doesn't cause any apparent issues. Optimising the
> spread of concurrent reclaimers for best efficiency can be done in a
> future patchset.

"Future patchset" as in "not in the 9 patches that I have left to read"?

> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_icache.c | 28 +++++++---------------------
> fs/xfs/xfs_mount.c | 4 ----
> fs/xfs/xfs_mount.h | 1 -
> 3 files changed, 7 insertions(+), 26 deletions(-)
>
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index ee9bc82a0dfbe..f44493b2eae77 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
> @@ -1226,12 +1226,9 @@ xfs_reclaim_inodes_ag(
> int *nr_to_scan)
> {
> struct xfs_perag *pag;
> - xfs_agnumber_t ag;
> - int trylock = flags & SYNC_TRYLOCK;
> - int skipped;
> + xfs_agnumber_t ag = 0;
> + int skipped = 0;
>
> - ag = 0;
> - skipped = 0;
> while ((pag = xfs_perag_get_tag(mp, ag, XFS_ICI_RECLAIM_TAG))) {
> unsigned long first_index = 0;
> int done = 0;
> @@ -1239,16 +1236,7 @@ xfs_reclaim_inodes_ag(
>
> ag = pag->pag_agno + 1;
>
> - if (trylock) {
> - if (!mutex_trylock(&pag->pag_ici_reclaim_lock)) {
> - skipped++;
> - xfs_perag_put(pag);
> - continue;
> - }
> - first_index = pag->pag_ici_reclaim_cursor;
> - } else
> - mutex_lock(&pag->pag_ici_reclaim_lock);
> -
> + first_index = READ_ONCE(pag->pag_ici_reclaim_cursor);
> do {
> struct xfs_inode *batch[XFS_LOOKUP_BATCH];
> int i;
> @@ -1313,11 +1301,9 @@ xfs_reclaim_inodes_ag(
>
> } while (nr_found && !done && *nr_to_scan > 0);
>
> - if (trylock && !done)
> - pag->pag_ici_reclaim_cursor = first_index;
> - else
> - pag->pag_ici_reclaim_cursor = 0;
> - mutex_unlock(&pag->pag_ici_reclaim_lock);
> + if (done)
> + first_index = 0;
> + WRITE_ONCE(pag->pag_ici_reclaim_cursor, first_index);
> xfs_perag_put(pag);
> }
> return skipped;
> @@ -1331,7 +1317,7 @@ xfs_reclaim_inodes(
> int nr_to_scan = INT_MAX;
> int skipped;
>
> - skipped = xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan);
> + xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan);

This could go in the previous patch, right?

The rest of this patch looks reasonable, so with that fixed,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> if (!(mode & SYNC_WAIT))
> return 0;
>
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index d5dcf98698600..03158b42a1943 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -148,7 +148,6 @@ xfs_free_perag(
> ASSERT(atomic_read(&pag->pag_ref) == 0);
> xfs_iunlink_destroy(pag);
> xfs_buf_hash_destroy(pag);
> - mutex_destroy(&pag->pag_ici_reclaim_lock);
> call_rcu(&pag->rcu_head, __xfs_free_perag);
> }
> }
> @@ -200,7 +199,6 @@ xfs_initialize_perag(
> pag->pag_agno = index;
> pag->pag_mount = mp;
> spin_lock_init(&pag->pag_ici_lock);
> - mutex_init(&pag->pag_ici_reclaim_lock);
> INIT_RADIX_TREE(&pag->pag_ici_root, GFP_ATOMIC);
> if (xfs_buf_hash_init(pag))
> goto out_free_pag;
> @@ -242,7 +240,6 @@ xfs_initialize_perag(
> out_hash_destroy:
> xfs_buf_hash_destroy(pag);
> out_free_pag:
> - mutex_destroy(&pag->pag_ici_reclaim_lock);
> kmem_free(pag);
> out_unwind_new_pags:
> /* unwind any prior newly initialized pags */
> @@ -252,7 +249,6 @@ xfs_initialize_perag(
> break;
> xfs_buf_hash_destroy(pag);
> xfs_iunlink_destroy(pag);
> - mutex_destroy(&pag->pag_ici_reclaim_lock);
> kmem_free(pag);
> }
> return error;
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index 3725d25ad97e8..a72cfcaa4ad12 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -354,7 +354,6 @@ typedef struct xfs_perag {
> spinlock_t pag_ici_lock; /* incore inode cache lock */
> struct radix_tree_root pag_ici_root; /* incore inode cache root */
> int pag_ici_reclaimable; /* reclaimable inodes */
> - struct mutex pag_ici_reclaim_lock; /* serialisation point */
> unsigned long pag_ici_reclaim_cursor; /* reclaim restart point */
>
> /* buffer cache index */
> --
> 2.26.2.761.g0e0b3e54be
>