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    SubjectRe: [PATCH v2 2/2] mm: memory_hotplug: introduce SECTION_CANNOT_OPTIMIZE_VMEMMAP
    On Fri, Jun 17, 2022 at 12:14:02PM +0200, David Hildenbrand wrote:
    > On 17.06.22 11:54, Oscar Salvador wrote:
    > > On Fri, Jun 17, 2022 at 09:43:33AM +0200, David Hildenbrand wrote:
    > >> VmemmapSelfHosted, then the function names get nicer.
    > >
    > > Definitely.
    > >
    > >>
    > >>> +#endif
    > >>> +
    > >>> /*
    > >>> * On an anonymous page mapped into a user virtual memory area,
    > >>> * page->mapping points to its anon_vma, not to a struct address_space;
    > >>> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
    > >>> index 1089ea8a9c98..e2de7ed27e9e 100644
    > >>> --- a/mm/hugetlb_vmemmap.c
    > >>> +++ b/mm/hugetlb_vmemmap.c
    > >>> @@ -101,6 +101,14 @@ void hugetlb_vmemmap_free(struct hstate *h, struct page *head)
    > >>> {
    > >>> unsigned long vmemmap_addr = (unsigned long)head;
    > >>> unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages;
    > >>> + struct mem_section *ms = __pfn_to_section(page_to_pfn(head));
    > >>> + struct page *memmap;
    > >>> +
    > >>> + memmap = sparse_decode_mem_map(ms->section_mem_map,
    > >>> + pfn_to_section_nr(page_to_pfn(head)));
    > >>
    > >> Why can't we check the head page directly? Either I need more coffee or
    > >> this can be simplified.
    > >
    > > Uhm, maybe I'm the one who needs coffe here but we have something like:
    > >
    > > [ hot-plugges section ]
    > > [memmap pages][normal pages]
    >
    > Oh, right, we need the memmap for our hugetlb page (which resides in the
    > reserved section), but these are not marked. We need the memmap of that
    > memmap.
    >
    > I assume one could directly via the page address. Because we want the
    > memmap of the memmap.
    >
    > vmmemmap_page = virt_to_page(head);
    >

    I think this can works, more simple.

    Thanks.

    > Not sure, though, if that would work with that function.

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