On Fri, Nov 17, 2023 at 12:08:31AM +0100, David Hildenbrand wrote: > On 14.11.23 19:02, Sumanth Korikkar wrote: > > Hi All, > > > > The patch series implements "memmap on memory" feature on s390 and > > provides the necessary fixes for it. > > Thinking about this, one thing that makes s390x different from all the other > architectures in this series is the altmap handling. > > I'm curious, why is that even required? > > A memmep that is not marked as online in the section should not be touched > by anybody (except memory onlining code :) ). And if we do, it's usually a > BUG because that memmap might contain garbage/be poisoned or completely > stale, so we might want to track that down and fix it in any case. > > So what speaks against just leaving add_memory() populate the memmap from > the altmap? Then, also the page tables for the memmap are already in place > when onlining memory. > we do have page_init_poison() in sparse_add_section() which should be handled later then. not in add_pages() > > Then, adding two new notifier calls on start of memory_block_online() called > something like MEM_PREPARE_ONLINE and end the end of memory_block_offline() > called something like MEM_FINISH_OFFLINE is still suboptimal, but that's > where standby memory could be activated/deactivated, without messing with > the altmap. > > That way, the only s390x specific thing is that the memmap that should not > be touched by anybody is actually inaccessible, and you'd > activate/deactivate simply from the new notifier calls just the way we used > to do. ok. Thanks
