Re: [PATCH v3 20/20] mm: stop maintaining the per-page mapcount of large folios (CONFIG_NO_PAGE_MAPCOUNT)
From: David Hildenbrand <hidden>
Date: 2025-10-20 13:53:12
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On 15.10.25 02:45, Wei Yang wrote:
On Tue, Oct 14, 2025 at 04:38:38PM +0200, David Hildenbrand wrote:quoted
On 14.10.25 16:32, Matthew Wilcox wrote:quoted
On Tue, Oct 14, 2025 at 02:59:30PM +0200, David Hildenbrand wrote:quoted
quoted
As commit 349994cf61e6 mentioned, we don't support partially mapped PUD-sized folio yet.We do support partially mapped PUD-sized folios I think, but not anonymous PUD-sized folios.I don't think so? The only mechanism I know of to allocate PUD-sized chunks of memory is hugetlb, and that doesn't permit partial mappings.Greetings from the latest DAX rework :)After a re-think, do you think it's better to align the behavior between CONFIG_NO_PAGE_MAPCOUNT and CONFIG_PAGE_MAPCOUNT? It looks we treat a PUD-sized folio partially_mapped if CONFIG_NO_PAGE_MAPCOUNT, but !partially_mapped if CONFIG_PAGE_MAPCOUNT, if my understanding is correct.
I'd just leave it alone unless there is a problem right now. -- Cheers David / dhildenb