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    SubjectRe: [PATCH v2 4/4] mm/vmalloc: Hugepage vmalloc mappings
    On Tue, Apr 14, 2020 at 02:28:35PM +0200, Christophe Leroy wrote:
    > Le 13/04/2020 à 15:41, Matthew Wilcox a écrit :
    > > On Mon, Apr 13, 2020 at 10:53:03PM +1000, Nicholas Piggin wrote:
    > > > +static int vmap_pages_range_noflush(unsigned long start, unsigned long end,
    > > > + pgprot_t prot, struct page **pages,
    > > > + unsigned int page_shift)
    > > > +{
    > > > + if (page_shift == PAGE_SIZE) {
    > >
    > > ... I think you meant 'page_shift == PAGE_SHIFT'
    > >
    > > Overall I like this series, although it's a bit biased towards CPUs
    > > which have page sizes which match PMD/PUD sizes. It doesn't offer the
    > > possibility of using 64kB page sizes on ARM, for example. But it's a
    > > step in the right direction.
    >
    > I was going to ask more or less the same question, I would have liked to use
    > 512kB hugepages on powerpc 8xx.
    >
    > Even the 8M hugepages (still on the 8xx), can they be used as well, taking
    > into account that two PGD entries have to point to the same 8M page ?
    >
    > I sent out a series which tends to make the management of 512k and 8M pages
    > closer to what Linux expects, in order to use them inside kernel, for Linear
    > mappings and Kasan mappings for the moment. See
    > https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=164620
    > It would be nice if we could amplify it a use it for ioremaps and vmallocs
    > as well.

    I haven't been looking at vmalloc at all; I've been looking at the page
    cache. See:
    https://lore.kernel.org/linux-mm/20200212041845.25879-1-willy@infradead.org/

    Once we have large pages in the page cache, I want to sort out the API
    for asking the CPU to insert a TLB entry. Right now, we use set_pte_at(),
    set_pmd_at() and set_pud_at(). I'm thinking something along the lines of:

    vm_fault_t vmf_set_page_at(struct vm_fault *vmf, struct page *page);

    and the architecture can insert whatever PTEs and/or TLB entries it
    likes based on compound_order(page) -- if, say, it's a 1MB page, it might
    choose to insert 2 * 512kB entries, or just the upper or lower 512kB entry
    (depending which half of the 1MB page the address sits in).

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