Re: [PATCH v7 1/8] xarray: add xas_try_split() to split a multi-index entry.

[David Hildenbrand <david@redhat.com>]

>>
>> Now, can it happen that xas_try_split() would ever perform a partial split in any way, when invoked from __split_unmapped_folio(), such that we run into the do { } while(); loop and fail with -ENOMEM after already having performed changes -- xas_update().
>>
>> Or is that simply impossible?
> 
> Right. It is impossible. xas_try_split() either splits by copying @entry
> to all the replacement entries, or is trying to allocate a new xa_node,
> which can result in -ENOMEM. These two will not be mixed.
> 
>>
>> Maybe it's just the do { } while(); loop in there that is confusing me. (again, no expert)
> 
> Yeah, that the do while loop is confusing. Let me restructure the code
> so that the do while loop only runs in the @entry copy case not the
> xa_node allocation case.

Great!

> 
>>
>>> xas_try_split() imposes what kind of split it does and is usually used to
>>> split from order N to order N-1:
>>
>> You mean that old_order -> split_order will in the case of __split_unmapped_folio() always be a difference of 1?
> 
> Yes for !uniform_split case. For uniform_split case (split_huge_page*() uses),
> xas_split() is used and all required new xa_node are preallocated by
> xas_split_alloc() in __folio_split().

Got it, thanks!

-- 
Cheers,

David / dhildenb