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

[Oscar Salvador <osalvador@suse.de>]

On 2021-03-15 10:06, David Hildenbrand wrote:
> BTW, I stumbled yesterday over
> 
> alloc_contig_pages()->pfn_range_valid_contig():
> 
> 	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 
can
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 
pages.

> 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 
pages.

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


-- 
Oscar Salvador
SUSE L3