Re: [PATCH 1/2] xfs: cap longest free extent to maximum allocatable

[Brian Foster <bfoster@redhat.com>]

On Wed, Sep 18, 2019 at 10:24:52AM +0200, Carlos Maiolino wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> Cap longest extent to the largest we can allocate based on limits
> calculated at mount time. Dynamic state (such as finobt blocks)
> can result in the longest free extent exceeding the size we can
> allocate, and that results in failure to align full AG allocations
> when the AG is empty.
> 
> Result:
> 
> xfs_io-4413  [003]   426.412459: xfs_alloc_vextent_loopfailed: dev 8:96 agno 0 agbno 32 minlen 243968 maxlen 244000 mod 0 prod 1 minleft 1 total 262148 alignment 32 minalignslop 0 len 0 type NEAR_BNO otype START_BNO wasdel 0 wasfromfl 0 resv 0 datatype 0x5 firstblock 0xffffffffffffffff
> 
> minlen and maxlen are now separated by the alignment size, and
> allocation fails because args.total > free space in the AG.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
> ---

Seems fine, but what about the bma.minlen alignment fix (in
xfs_bmap_btalloc()) Dave suggested in the previous thread?

Brian

>  fs/xfs/libxfs/xfs_alloc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index 372ad55631fc..35b39fc863a0 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -1989,7 +1989,8 @@ xfs_alloc_longest_free_extent(
>  	 * reservations and AGFL rules in place, we can return this extent.
>  	 */
>  	if (pag->pagf_longest > delta)
> -		return pag->pagf_longest - delta;
> +		return min_t(xfs_extlen_t, pag->pag_mount->m_ag_max_usable,
> +				pag->pagf_longest - delta);
>  
>  	/* Otherwise, let the caller try for 1 block if there's space. */
>  	return pag->pagf_flcount > 0 || pag->pagf_longest > 0;
> -- 
> 2.20.1
>