This series is based on the latest s390/features branch [1]. It consolidates vmem_add_range(), vmem_remove_range(), and vmemmap_populate() into a single, recursive page table walker. It then implements vmemmap_free() and optimizes it by - Freeing empty page tables (also done for vmem_remove_range()). - Handling cases where the vmemmap of a section does not fill huge pages completely (e.g., sizeof(struct page) == 56). vmemmap_free() is currently never used, unless adiing standby memory fails (unlikely). This is relevant for virtio-mem, which adds/removes memory in memory block/section granularity (always removes memory in the same granularity it added it). I gave this a proper test with my virtio-mem prototype (which I will share in the near future), both with 56 byte memmap per page and 64 byte memmap per page, with and without huge page support. In both cases, removing memory (routed through arch_remove_memory()) will result in - all populated vmemmap pages to get removed/freed - all applicable page tables for the vmemmap getting removed/freed - all applicable page tables for the idendity mapping getting removed/freed Unfortunately, I don't have access to bigger and z/VM (esp. dcss) environments. This is the basis for real memory hotunplug support for s390x and should complete my journey to s390x vmem/vmemmap code for now What needs double-checking is tlb flushing. AFAIKS, as there are no valid accesses, doing a single range flush at the end is sufficient, both when removing vmemmap pages and the idendity mapping. [1] https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git/commit/?h=features v1 -> v2: - Convert to a single page table walker named "modify_pagetable()", with two helper functions "add_pagetable()" and "remove_pagetable(). David Hildenbrand (9): s390/vmem: rename vmem_add_mem() to vmem_add_range() s390/vmem: consolidate vmem_add_range() and vmem_remove_range() s390/vmemmap: extend modify_pagetable() to handle vmemmap s390/vmemmap: cleanup when vmemmap_populate() fails s390/vmemmap: take the vmem_mutex when populating/freeing s390/vmem: cleanup empty page tables s390/vmemmap: fallback to PTEs if mapping large PMD fails s390/vmemmap: remember unused sub-pmd ranges s390/vmemmap: avoid memset(PAGE_UNUSED) when adding consecutive sections arch/s390/mm/vmem.c | 637 ++++++++++++++++++++++++++++++-------------- 1 file changed, 442 insertions(+), 195 deletions(-) -- 2.26.2
