On Fri, Jun 11, 2021 at 12:48:26PM -0700, Nathan Chancellor wrote:
> Hi all,
> 
> I am occasionally seeing a kernel warning when running virtual machines
> in Hyper-V, which usually happens a minute or so after boot. It does not
> happen on every boot and it is reproducible on at least v5.10. I think
> it might have something to do with constant reboots, which I do when
> testing various kernels.
> 
> The stack trace is as follows:
> 
> [   49.215291] kworker/0:1: vmemmap alloc failure: order:9, mode:0x4cc0(GFP_KERNEL|__GFP_RETRY_MAYFAIL), nodemask=(null),cpuset=/,mems_allowed=0
> [   49.215299] CPU: 0 PID: 18 Comm: kworker/0:1 Not tainted 5.13.0-rc5 #1
> [   49.215301] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.0 11/01/2019
> [   49.215302] Workqueue: events hot_add_req [hv_balloon]
> [   49.215307] Call Trace:
> [   49.215310]  dump_stack+0x76/0x94
> [   49.215314]  warn_alloc.cold+0x78/0xdc
> [   49.215316]  ? __alloc_pages+0x200/0x230
> [   49.215319]  vmemmap_alloc_block+0x86/0xdc
> [   49.215323]  vmemmap_populate+0x10e/0x31c
> [   49.215324]  __populate_section_memmap+0x38/0x4e
> [   49.215326]  sparse_add_section+0x12c/0x1cf
> [   49.215329]  __add_pages+0xa9/0x130
> [   49.215330]  add_pages+0x12/0x60
> [   49.215333]  add_memory_resource+0x180/0x300
> [   49.215335]  __add_memory+0x3b/0x80
> [   49.215336]  add_memory+0x2e/0x50
> [   49.215337]  hot_add_req+0x3fc/0x5a0 [hv_balloon]
> [   49.215340]  process_one_work+0x214/0x3e0
> [   49.215342]  worker_thread+0x4d/0x3d0
> [   49.215344]  ? process_one_work+0x3e0/0x3e0
> [   49.215345]  kthread+0x133/0x150
> [   49.215347]  ? kthread_associate_blkcg+0xc0/0xc0
> [   49.215348]  ret_from_fork+0x22/0x30
> [   49.215351] Mem-Info:
> [   49.215352] active_anon:251 inactive_anon:140868 isolated_anon:0
>                 active_file:47497 inactive_file:88505 isolated_file:0
>                 unevictable:8 dirty:14 writeback:0
>                 slab_reclaimable:12013 slab_unreclaimable:11403
>                 mapped:131701 shmem:12671 pagetables:3140 bounce:0
>                 free:41388 free_pcp:37 free_cma:0
> [   49.215355] Node 0 active_anon:1004kB inactive_anon:563472kB active_file:189988kB inactive_file:354020kB unevictable:32kB isolated(anon):0kB isolated(file):0kB mapped:526804kB dirty:56kB writeback:0kB shmem:50684kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 0kB writeback_tmp:0kB kernel_stack:5904kB pagetables:12560kB all_unreclaimable? no
> [   49.215358] Node 0 DMA free:6496kB min:480kB low:600kB high:720kB reserved_highatomic:0KB active_anon:0kB inactive_anon:3120kB active_file:2584kB inactive_file:2792kB unevictable:0kB writepending:0kB present:15996kB managed:15360kB mlocked:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
> [   49.215361] lowmem_reserve[]: 0 1384 1384 1384 1384
> [   49.215364] Node 0 DMA32 free:159056kB min:44572kB low:55712kB high:66852kB reserved_highatomic:0KB active_anon:1004kB inactive_anon:560352kB active_file:187004kB inactive_file:350864kB unevictable:32kB writepending:56kB present:1555760kB managed:1432388kB mlocked:32kB bounce:0kB free_pcp:172kB local_pcp:0kB free_cma:0kB
> [   49.215367] lowmem_reserve[]: 0 0 0 0 0
> [   49.215369] Node 0 DMA: 17*4kB (UM) 13*8kB (M) 10*16kB (M) 3*32kB (ME) 3*64kB (UME) 4*128kB (UME) 1*256kB (E) 2*512kB (UE) 2*1024kB (ME) 1*2048kB (E) 0*4096kB = 6508kB
> [   49.215377] Node 0 DMA32: 8061*4kB (UME) 5892*8kB (UME) 2449*16kB (UME) 604*32kB (UME) 207*64kB (UME) 49*128kB (UM) 7*256kB (M) 1*512kB (M) 0*1024kB 0*2048kB 0*4096kB = 159716kB
> [   49.215388] 148696 total pagecache pages
> [   49.215388] 0 pages in swap cache
> [   49.215389] Swap cache stats: add 0, delete 0, find 0/0
> [   49.215390] Free swap  = 0kB
> [   49.215390] Total swap = 0kB
> [   49.215391] 392939 pages RAM
> [   49.215391] 0 pages HighMem/MovableOnly
> [   49.215391] 31002 pages reserved
> [   49.215392] 0 pages cma reserved
> [   49.215393] 0 pages hwpoisoned
> 
> Is this a known issue and/or am I doing something wrong? I only noticed
> this because there are times when I am compiling something intensive in
> the VM such as LLVM and the VM runs out of memory even though I have
> plenty of free memory on the host but I am not sure if this warning is
> related to that issue.

I had one of these events just happen, journalctl output attached. I
have no idea what the "unhandled message: type:" messages mean, I guess
that corresponds to the switch statement in balloon_onchannelcallback().

> I do not have much experience with Hyper-V so it is possible I do not
> have something configured properly or there is some other issue going
> on. Let me know if there is any further information I can provide or
> help debug in any way.

Cheers,
Nathan