On Fri, Nov 6, 2020 at 5:46 PM Oscar Salvador <osalvador@xxxxxxx> wrote: > > On Fri, Nov 06, 2020 at 12:08:22AM +0800, Muchun Song wrote: > > > I do not think you need this. > > > We already have hugepages_supported(). > > > > Maybe some architectures support hugepage, but the vmemmap do not > > use the hugepage map. In this case, we need it. But I am not sure if it > > exists in the real world. At least, x86 can reuse hugepages_supported. > > Yes, but that is the point. > IIUC, this patchset will enable HugeTLB vmemmap pages only for x86_64. > Then, let us make the patchset specific to that architecture. > > If at some point this grows more users (powerpc, arm, ...), then we > can add the missing code, but for now it makes sense to only include > the bits to make this work on x86_64. > > And also according to this the changelog is a bit "misleading". > > "On some architectures, the vmemmap areas use huge page mapping. > If we want to free the unused vmemmap pages, we have to split > the huge pmd firstly. So we should pre-allocate pgtable to split > huge pmd." Thanks for your suggestions. I will rewrite the commit log. > > On x86_64, vmemmap is always PMD mapped if the machine has hugepages > support and if we have 2MB contiguos pages and PMD aligned. > e.g: I have seen cases where after the system has ran for a period > of time hotplug operations were mapping the vmemmap representing > the hot-added range on page base, because we could not find > enough contiguos and aligned memory. > > Something that [1] tries to solve: > > [1] https://patchwork.kernel.org/project/linux-mm/cover/20201022125835.26396-1-osalvador@xxxxxxx/ > > But anyway, my point is that let us make it clear in the changelog that > this is aimed for x86_64 at the moment. > Saying "on some architures" might make think people that this is not > x86_64 specific. > > >> > > + vmemmap_pgtable_init(page); > > > > > > Maybe just open code this one? > > > > Sorry. I don't quite understand what it means. Could you explain? > > I meant doing > > page_huge_pte(page) = NULL > > But no strong feelings. > > -- > Oscar Salvador > SUSE L3 -- Yours, Muchun
