Re: [RFC PATCH v2 4/7] mm: pgtable: try to reclaim empty PTE pages in zap_page_range_single()

[David Hildenbrand <david@redhat.com>]

>>
>> (b) if we didn't have to drop the PTL, we can remove the page table
>>       without even re-verifying whether the entries are pte_none(). We
> 
> If we want to remove the PTE page, we must hold the pmd lock (for
> clearing pmd entry). To prevent ABBA deadlock, we must first release the
> pte lock and then re-acquire the pmd lock + pte lock. Right? If so, then
> rechecking pte_none() is unavoidable. Unless we hold the pmd lock + pte
> lock in advance to execute the original code loop.

Try-locking the PMD should work, and succeed in many cases, right? And 
if that fails, we could fallback to what you describe.

-- 
Cheers,

David / dhildenb