Re: [PATCH v2 08/10] mm/hugetlb: Make walk_hugetlb_range() safe to pmd unshare

Peter Xu
2022-12-09T14:40:36Z

On Fri, Dec 09, 2022 at 11:24:55AM +0100, David Hildenbrand wrote:
> For such cases, it would be good to have any evidence that it really helps.

I don't know much on the s390 path, but if a process has a large hugetlb
vma, even MADV_DONTNEED will be blocked for whatever long time if there's
another process or thread scanning pagemap for this vma.

Would this justify a bit?

It's just that the vma lock is taken write far more than mmap_lock taken
write I think, meanwhile what we need here is only release the lock and
retake, nothing else. It didn't make things over complicated, IMO.

No strong ipinion from my side, as I said to me it's really low hanging
fruit. If you still think that doesn't justify and if Mike doesn't have a
preference either I can just drop it for later.

--
Peter Xu