On 11.05.22 18:10, HORIGUCHI NAOYA(堀口 直也) wrote: > On Wed, May 11, 2022 at 05:11:17PM +0200, David Hildenbrand wrote: >> On 09.05.22 12:53, Miaohe Lin wrote: >>> On 2022/5/9 17:58, Oscar Salvador wrote: >>>> On Mon, May 09, 2022 at 05:04:54PM +0800, Miaohe Lin wrote: >>>>>>> So that leaves us with either >>>>>>> >>>>>>> 1) Fail offlining -> no need to care about reonlining >>>>> >>>>> Maybe fail offlining will be a better alternative as we can get rid of many races >>>>> between memory failure and memory offline? But no strong opinion. :) >>>> >>>> If taking care of those races is not an herculean effort, I'd go with >>>> allowing offlining + disallow re-onlining. >>>> Mainly because memory RAS stuff. >>> >>> This dose make sense to me. Thanks. We can try to solve those races if >>> offlining + disallow re-onlining is applied. :) >>> >>>> >>>> Now, to the re-onlining thing, we'll have to come up with a way to check >>>> whether a section contains hwpoisoned pages, so we do not have to go >>>> and check every single page, as that will be really suboptimal. >>> >>> Yes, we need a stable and cheap way to do that. >> >> My simplistic approach would be a simple flag/indicator in the memory block devices >> that indicates that any page in the memory block was hwpoisoned. It's easy to >> check that during memory onlining and fail it. >> >> diff --git a/drivers/base/memory.c b/drivers/base/memory.c >> index 084d67fd55cc..3d0ef812e901 100644 >> --- a/drivers/base/memory.c >> +++ b/drivers/base/memory.c >> @@ -183,6 +183,9 @@ static int memory_block_online(struct memory_block *mem) >> struct zone *zone; >> int ret; >> >> + if (mem->hwpoisoned) >> + return -EHWPOISON; >> + >> zone = zone_for_pfn_range(mem->online_type, mem->nid, mem->group, >> start_pfn, nr_pages); >> > > Thanks for the idea, a simple flag could work if we don't have to consider > unpoison. If we need consider unpoison, we need remember the last hwpoison > page in the memory block, so mem->hwpoisoned should be the counter of > hwpoison pages. Right, but unpoisoning+memory offlining+memory onlining is a yet more extreme use case we don't have to bother about I think. > >> >> >> Once the problematic DIMM would actually get unplugged, the memory block devices >> would get removed as well. So when hotplugging a new DIMM in the same >> location, we could online that memory again. > > What about PG_hwpoison flags? struct pages are also freed and reallocated > in the actual DIMM replacement? Once memory is offline, the memmap is stale and is no longer trustworthy. It gets reinitialize during memory onlining -- so any previous PG_hwpoison is overridden at least there. In some setups, we even poison the whole memmap via page_init_poison() during memory offlining. Apart from that, we should be freeing the memmap in all relevant cases when removing memory. I remember there are a couple of corner cases, but we don't really have to care about that. -- Thanks, David / dhildenb