[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] xen/balloon: fix page onlining when populating new zone
On Thu, Apr 07, 2022 at 11:00:33AM +0200, David Hildenbrand wrote: >On 07.04.22 10:50, Juergen Gross wrote: >> On 07.04.22 10:23, David Hildenbrand wrote: >>> On 06.04.22 15:32, Juergen Gross wrote: >>>> When onlining a new memory page in a guest the Xen balloon driver is >>>> adding it to the ballooned pages instead making it available to be >>>> used immediately. This is meant to enable to add a new upper memory >>>> limit to a guest via hotplugging memory, without having to assign the >>>> new memory in one go. >>>> >>>> In case the upper memory limit will be raised above 4G, the new memory >>>> will populate the ZONE_NORMAL memory zone, which wasn't populated >>>> before. The newly populated zone won't be added to the list of zones >>>> looked at by the page allocator though, as only zones with available >>>> memory are being added, and the memory isn't yet available as it is >>>> ballooned out. >>> >>> I think we just recently discussed these corner cases on the -mm list. >> >> Indeed. >> >>> The issue is having effectively populated zones without manages pages >>> because everything is inflated in a balloon. >> >> Correct. >> >>> That can theoretically also happen when managing to fully inflate the >>> balloon in one zone and then, somehow, the zones get rebuilt. >> >> I think you are right. I didn't think of that scenario. >> >>> build_zonerefs_node() documents "Add all populated zones of a node to >>> the zonelist" but checks for managed zones, which is wrong. >>> >>> See https://lkml.kernel.org/r/20220201070044.zbm3obsoimhz3xd3@master >> >> I found commit 6aa303defb7454 which introduced this test. I thought >> it was needed due to the problem this commit tried to solve. Maybe I >> was wrong and that commit shouldn't have changed the condition when >> building the zonelist, but just the ones in the allocation paths. > >In regard to kswapd, that is currently being worked on via > >https://lkml.kernel.org/r/20220329010901.1654-2-richard.weiyang@xxxxxxxxx > Thanks, David Do you think it is the right time to repost the original fix? >-- >Thanks, > >David / dhildenb -- Wei Yang Help you, Help me
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