On Wed, May 11, 2022 at 06:22:41PM +0200, 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. OK. Maybe starting with simple one is fine. > > > > >> > >> > >> 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. OK, so there seems no need to manipulate struct pages for hwpoison in all relevant cases. Thanks, Naoya Horiguchi
