xfs: queue inactivation immediately when free space is tight

Now that we have made the inactivation of unlinked inodes a background
task to increase the throughput of file deletions, we need to be a
little more careful about how long of a delay we can tolerate.

On a mostly empty filesystem, the risk of the allocator making poor
decisions due to fragmentation of the free space on account a lengthy
delay in background updates is minimal because there's plenty of space.
However, if free space is tight, we want to deallocate unlinked inodes
as quickly as possible to avoid fallocate ENOSPC and to give the
allocator the best shot at optimal allocations for new writes.

Therefore, queue the percpu worker immediately if the filesystem is more
than 95% full.  This follows the same principle that XFS becomes less
aggressive about speculative allocations and lazy cleanup (and more
precise about accounting) when nearing full.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/xfs_mount.c

@@ -1077,14 +1077,6 @@ xfs_fs_writable(
 	return true;
 }
 
-/*
- * Deltas for the block count can vary from 1 to very large, but lock contention
- * only occurs on frequent small block count updates such as in the delayed
- * allocation path for buffered writes (page a time updates). Hence we set
- * a large batch count (1024) to minimise global counter updates except when
- * we get near to ENOSPC and we have to be very accurate with our updates.
- */
-#define XFS_FDBLOCKS_BATCH	1024
 int
 xfs_mod_fdblocks(
 	struct xfs_mount	*mp,