On Wed, Jul 22, 2020 at 11:45:49AM +0200, David Hildenbrand wrote: > 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(-) Series applied, thank you!
