Re: vmemmap alloc failure in hot_add_req()

[David Hildenbrand <david@redhat.com>]

On 12.06.21 04:11, Hillf Danton wrote:
> On Fri, 11 Jun 2021 12:48:26 -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]
> 
> Apart from order:9 (mm Cced), events_unbound is the right workqueue instead
> because the report shows the risk that hot_add_req could block other pending
> events longer than thought. Any special reason for the events wq?
> 
>> [   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.

Hi,

Is hotplugged memory getting onlined automatically (either from user 
space via a udev script or via the kernel, for example, with 
CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE)?

If it's not getting onlined, you easily sport after hotplug e.g., via 
"lsmem" that there are quite some offline memory blocks.

Note that x86_64 code will fallback from populating huge pages to 
populating base pages for the vmemmap; this can happen easily when under 
memory pressure.

If adding memory would fail completely, you'd see another "hot_add 
memory failed error is ..." error message from hyper-v in the kernel 
log. If that doesn't show up, it's simply suboptimal, but hotplugging 
memory still succeeded.


Note: we could support "memmap_on_memory" in some cases (e.g., no memory 
holes in hotadded range) when hotplugging memory blocks via hyper-v, 
which would result in this warning less trigger less frequently.

-- 
Thanks,

David / dhildenb