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

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On Wed, Sep 18, 2019 at 08:27:26AM -0400, Brian Foster wrote:
> On Wed, Sep 18, 2019 at 10:24:52AM +0200, Carlos Maiolino wrote:
> > From: Dave Chinner <dchinner@xxxxxxxxxx>
> > 
> > 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@xxxxxxxxxx>
> > Signed-off-by: Carlos Maiolino <cmaiolino@xxxxxxxxxx>
> > ---
> 
> Seems fine, but what about the bma.minlen alignment fix (in
> xfs_bmap_btalloc()) Dave suggested in the previous thread?

I forgot to git add that while playing with this set :P

> 
> 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
> > 

-- 
Carlos



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