On 04/04/2019 08:07, Anshuman Khandual wrote: > > > On 04/03/2019 11:02 PM, Logan Gunthorpe wrote: >> >> >> On 2019-04-02 10:30 p.m., Anshuman Khandual wrote: >>> Memory removal from an arch perspective involves tearing down two different >>> kernel based mappings i.e vmemmap and linear while releasing related page >>> table pages allocated for the physical memory range to be removed. >>> >>> Define a common kernel page table tear down helper remove_pagetable() which >>> can be used to unmap given kernel virtual address range. In effect it can >>> tear down both vmemap or kernel linear mappings. This new helper is called >>> from both vmemamp_free() and ___remove_pgd_mapping() during memory removal. >>> The argument 'direct' here identifies kernel linear mappings. >>> >>> Vmemmap mappings page table pages are allocated through sparse mem helper >>> functions like vmemmap_alloc_block() which does not cycle the pages through >>> pgtable_page_ctor() constructs. Hence while removing it skips corresponding >>> destructor construct pgtable_page_dtor(). >>> >>> While here update arch_add_mempory() to handle __add_pages() failures by >>> just unmapping recently added kernel linear mapping. Now enable memory hot >>> remove on arm64 platforms by default with ARCH_ENABLE_MEMORY_HOTREMOVE. >>> >>> This implementation is overall inspired from kernel page table tear down >>> procedure on X86 architecture. >> >> I've been working on very similar things for RISC-V. In fact, I'm >> currently in progress on a very similar stripped down version of >> remove_pagetable(). (Though I'm fairly certain I've done a bunch of >> stuff wrong.) >> >> Would it be possible to move this work into common code that can be used >> by all arches? Seems like, to start, we should be able to support both >> arm64 and RISC-V... and maybe even x86 too. >> >> I'd be happy to help integrate and test such functions in RISC-V. > > Sure that will be great. The only impediment is pgtable_page_ctor() for kernel > linear mapping. This series is based on current arm64 where linear mapping > pgtable pages go through pgtable_page_ctor() init sequence but that might be > changing soon. If RISC-V does not have pgtable_page_ctor() init for linear > mapping and no other arch specific stuff later on we can try to consolidate > remove_pagetable() atleast for both the architectures. > > Then I wondering whether I can transition pud|pmd_large() to pud|pmd_sect(). The first 10 patches of my generic page walk series[1] adds p?d_large() as a common feature, so probably best sticking with p?d_large() if this is going to be common and basing on top of those patches. [1] https://lore.kernel.org/lkml/20190403141627.11664-1-steven.price@xxxxxxx/T/ Steve
