Re: [PATCH 03/16] xfs: finobt AG reserves don't consider last AG can be a runt

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Nov 07, 2018 at 05:31:14PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> The last AG may be very small comapred to all other AGs, and hence
> AG reservations based on the superblock AG size may actually consume
> more space than the AG actually has. This results on assert failures
> like:
> 
> XFS: Assertion failed: xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved + xfs_perag_resv(pag, XFS_AG_RESV_RMAPBT)->ar_reserved <= pag->pagf_freeblks + pag->pagf_flcount, file: fs/xfs/libxfs/xfs_ag_resv.c, line: 319
> [   48.932891]  xfs_ag_resv_init+0x1bd/0x1d0
> [   48.933853]  xfs_fs_reserve_ag_blocks+0x37/0xb0
> [   48.934939]  xfs_mountfs+0x5b3/0x920
> [   48.935804]  xfs_fs_fill_super+0x462/0x640
> [   48.936784]  ? xfs_test_remount_options+0x60/0x60
> [   48.937908]  mount_bdev+0x178/0x1b0
> [   48.938751]  mount_fs+0x36/0x170
> [   48.939533]  vfs_kern_mount.part.43+0x54/0x130
> [   48.940596]  do_mount+0x20e/0xcb0
> [   48.941396]  ? memdup_user+0x3e/0x70
> [   48.942249]  ksys_mount+0xba/0xd0
> [   48.943046]  __x64_sys_mount+0x21/0x30
> [   48.943953]  do_syscall_64+0x54/0x170
> [   48.944835]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Hence we need to ensure the finobt per-ag space reservations take
> into account the size of the last AG rather than treat it like all
> the other full size AGs.
> 
> Note that both refcountbt and rmapbt already take the size of the AG
> into account via reading the AGF length directly.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/libxfs/xfs_ialloc_btree.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_ialloc_btree.c b/fs/xfs/libxfs/xfs_ialloc_btree.c
> index 86c50208a143..62014780d5e4 100644
> --- a/fs/xfs/libxfs/xfs_ialloc_btree.c
> +++ b/fs/xfs/libxfs/xfs_ialloc_btree.c
> @@ -538,15 +538,24 @@ xfs_inobt_rec_check_count(
>  
>  static xfs_extlen_t
>  xfs_inobt_max_size(
> -	struct xfs_mount	*mp)
> +	struct xfs_mount	*mp,
> +	xfs_agnumber_t		agno)
>  {
> +	uint32_t		agblocks = mp->m_sb.sb_agblocks;
> +
>  	/* Bail out if we're uninitialized, which can happen in mkfs. */
>  	if (mp->m_inobt_mxr[0] == 0)
>  		return 0;
>  
> +	/* last AG can be a runt */
> +	if (agno == mp->m_sb.sb_agcount - 1) {
> +		div_u64_rem(mp->m_sb.sb_dblocks, mp->m_sb.sb_agblocks,
> +				&agblocks);
> +	}

Why not: agblocks = xfs_ag_block_count(mp, agno); ?

--D

> +
>  	return xfs_btree_calc_size(mp->m_inobt_mnr,
> -		(uint64_t)mp->m_sb.sb_agblocks * mp->m_sb.sb_inopblock /
> -				XFS_INODES_PER_CHUNK);
> +				(uint64_t)agblocks * mp->m_sb.sb_inopblock /
> +					XFS_INODES_PER_CHUNK);
>  }
>  
>  static int
> @@ -594,7 +603,7 @@ xfs_finobt_calc_reserves(
>  	if (error)
>  		return error;
>  
> -	*ask += xfs_inobt_max_size(mp);
> +	*ask += xfs_inobt_max_size(mp, agno);
>  	*used += tree_len;
>  	return 0;
>  }
> -- 
> 2.19.1
>