On 2022/5/12 0:22, David Hildenbrand wrote: > 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. > I tend to agree with David. The memmap is unreliable after memory is offline. So preventing memory re-online until a new DIMM replacement is a good idea. Thanks! > 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. >
