Re: [PATCH v4 0/4] Make alloc_contig_range handle Hugetlb pages

From: David Hildenbrand
Date: Wed Mar 17 2021 - 05:49:26 EST

On 17.03.21 10:43, Oscar Salvador wrote:
On 2021-03-15 10:06, David Hildenbrand wrote:
BTW, I stumbled yesterday over


if (page_count(page) > 0)
rerurn false;
if (PageHuge(page))
return false;

As used by memtrace and for gigantic pages. We can now

a) Drop these check completely, as it's best-effort only and racy.
alloc_contig_pages()/alloc_contig_range() will handle it properly.

I was preparing v5, and I wanted to be sure I understood you here.

Right you are that the in-use page check can be dropped, as those pages
be migrated away, and the Hugetlb page check can also be dropped since
isolate_migratepages_range is now capable of dealing with those kind of

b) Similarly, check for gigantic pages and/or movability/migratability.

I lost you here.

isolate_or_dissolve_huge_page() already bails out on hugetlb-gigantic

Or do you mean to place an upfront check here? (hstate_is_gigantic())?

Yes. But I prefer a) and keeping it simple here -- just doing basic sanity checks (online, zone, PageReserved()) that are absolutely necessary.


David / dhildenb