On 07.07.20 14:08, Heiko Carstens wrote: > On Fri, Jul 03, 2020 at 03:39:08PM +0200, David Hildenbrand wrote: >> This series is based on the latest s390/features branch [1]. It implements >> vmemmap_free(), consolidating it with vmem_add_range(), and optimizes it by >> - Freeing empty page tables (now also done for idendity mapping). >> - Handling cases where the vmemmap of a section does not fill huge pages >> completely. >> >> 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 >> once the basic QEMU implementation is upstream), 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. >> >> Along, some minor cleanups. > > Hmm.. I really would like to see if there would be only a single page > table walker left in vmem.c, which handles both adding and removing > things. > Now we end up with two different page table walk implementations > within the same file. However not sure if it is worth the effort to > unify them though. I tried to unify vmemmap_populate() and vmem_add_range() already and didn't like the end result ... so, unifying these along with the removal part won't be any better - most probably. Open for suggestions :) (at least arm64 and x86-64 handle it similarly) -- Thanks, David / dhildenb
