Re: [PATCH 3/7] xfs: defer agfl block frees when dfops is available

[Christoph Hellwig <hch@infradead.org>]

> Add the capability to defer AGFL block frees when a deferred ops
> list is available to the AGFL fixup code.

When is one available and when not?  Why are we fine not delaying it
in some cases?

> Note that this patch only adds infrastructure. It does not change
> behavior because no callers have been updated to pass ->t_dfops into
> the allocation code.

So the plan is to eventually have all callers pass it?  If so that is
another argument to first always pass defer_ops through the transaction,
then make sure all callers have it where required, and only then move
to actually use it.

> +{
> +	struct xfs_extent_free_item	*new;		/* new element */
> +
> +	ASSERT(xfs_bmap_free_item_zone != NULL);
> +	ASSERT(oinfo != NULL);

No need for either assert, we get nice clean NULL ptr dereferences when
this isn't true.