Re: [PATCH] xfs: tune down agno asserts in the bmap code

[Christoph Hellwig <hch@lst.de>]

On Thu, Feb 16, 2017 at 05:11:17PM -0800, Darrick J. Wong wrote:
> On Thu, Feb 16, 2017 at 10:10:35PM +0100, Christoph Hellwig wrote:
> > In various places we currently assert that xfs_bmap_btalloc allocates
> > from the same as the firstblock value passed in, unless it's either
> > NULLAGNO or the dop_low flag is set.  But the reflink code does not
> > fully follow this convention as it passes in firstblock purely as
> > a hint for the allocator without actually having previous allocations
> 
> Are you referring to BMAPI_REMAP?

Yes.

> In that case *firstblock isn't a
> hint, it's the new physical location of the extent.

Yes and no.  For the high-level bmap code it is indeed the location of the
extent, but it then also gets passed down to the btree code, where is
is treated as both a hint for allocating the bmap btree blocks close
to it, which limits the allocation to the same AG.  We work around that
a bit using the try_another_ag loop, but it's all a bit of a mess.

> By the way, was it your intent to push this series into 4.11?

It's just a single patch, and given that it's fairly easy to trigger
we should defintively have it in 4.11 and later -stable.