Re: [PATCH 18/30] xfs: remove IO submission from xfs_reclaim_inode()

[Brian Foster <bfoster@redhat.com>]

On Thu, Jun 04, 2020 at 05:45:54PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> We no longer need to issue IO from shrinker based inode reclaim to
> prevent spurious OOM killer invocation. This leaves only the global
> filesystem management operations such as unmount needing to
> writeback dirty inodes and reclaim them.
> 
> Instead of using the reclaim pass to write dirty inodes before
> reclaiming them, use the AIL to push all the dirty inodes before we
> try to reclaim them. This allows us to remove all the conditional
> SYNC_WAIT locking and the writeback code from xfs_reclaim_inode()
> and greatly simplify the checks we need to do to reclaim an inode.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/xfs_icache.c | 117 ++++++++++++--------------------------------
>  1 file changed, 31 insertions(+), 86 deletions(-)
> 
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index a6780942034fc..74032316ce5cc 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
...
> @@ -1341,9 +1288,8 @@ xfs_reclaim_inodes_ag(
>  			for (i = 0; i < nr_found; i++) {
>  				if (!batch[i])
>  					continue;
> -				error = xfs_reclaim_inode(batch[i], pag, flags);
> -				if (error && last_error != -EFSCORRUPTED)
> -					last_error = error;
> +				if (!xfs_reclaim_inode(batch[i], pag, flags))
> +					skipped++;

Just a note that I find it a little bit of a landmine that skipped is
bumped on trylock failure of the perag reclaim lock when the
xfs_reclaim_inodes() caller can now spin on that. It doesn't appear to
be an issue with current users, though (xfs_reclaim_workers() passes
SYNC_TRYLOCK but not SYNC_WAIT).

>  			}
>  
>  			*nr_to_scan -= XFS_LOOKUP_BATCH;
...
> @@ -1380,8 +1314,18 @@ xfs_reclaim_inodes(
>  	int		mode)
>  {
>  	int		nr_to_scan = INT_MAX;
> +	int		skipped;
>  
> -	return xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan);
> +	xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan);
> +	if (!(mode & SYNC_WAIT))
> +		return 0;
> +

Any reason we fall into the loop below if SYNC_WAIT was passed but the
above xfs_reclaim_inodes_ag() call would have returned 0?

Looks reasonable other than that inefficiency:

Reviewed-by: Brian Foster <bfoster@redhat.com>

> +	do {
> +		xfs_ail_push_all_sync(mp->m_ail);
> +		skipped = xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan);
> +	} while (skipped > 0);
> +
> +	return 0;
>  }
>  
>  /*
> @@ -1402,7 +1346,8 @@ xfs_reclaim_inodes_nr(
>  	xfs_reclaim_work_queue(mp);
>  	xfs_ail_push_all(mp->m_ail);
>  
> -	return xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK, &nr_to_scan);
> +	xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK, &nr_to_scan);
> +	return 0;
>  }
>  
>  /*
> -- 
> 2.26.2.761.g0e0b3e54be
>