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SubjectRe: [RFC PATCH 0/2] mm: fix OOMs for binding workloads to movable zone only node
Date
On 11/5/20 1:58 PM, Michal Hocko wrote:
> On Thu 05-11-20 13:53:24, Vlastimil Babka wrote:
>> On 11/5/20 1:08 PM, Michal Hocko wrote:
>> > On Thu 05-11-20 09:40:28, Feng Tang wrote:
>> > > > > Could you be more specific? This sounds like a bug. Allocations
>> > > > shouldn't spill over to a node which is not in the cpuset. There are few
>> > > > exceptions like IRQ context but that shouldn't happen regurarly.
>> > >
>> > > I mean when the docker starts, it will spawn many processes which obey
>> > > the mem binding set, and they have some kernel page requests, which got
>> > > successfully allocated, like the following callstack:
>> > >
>> > > [ 567.044953] CPU: 1 PID: 2021 Comm: runc:[1:CHILD] Tainted: G W I 5.9.0-rc8+ #6
>> > > [ 567.044956] Hardware name: /NUC6i5SYB, BIOS SYSKLi35.86A.0051.2016.0804.1114 08/04/2016
>> > > [ 567.044958] Call Trace:
>> > > [ 567.044972] dump_stack+0x74/0x9a
>> > > [ 567.044978] __alloc_pages_nodemask.cold+0x22/0xe5
>> > > [ 567.044986] alloc_pages_current+0x87/0xe0
>> > > [ 567.044991] allocate_slab+0x2e5/0x4f0
>> > > [ 567.044996] ___slab_alloc+0x380/0x5d0
>> > > [ 567.045021] __slab_alloc+0x20/0x40
>> > > [ 567.045025] kmem_cache_alloc+0x2a0/0x2e0
>> > > [ 567.045033] mqueue_alloc_inode+0x1a/0x30
>> > > [ 567.045041] alloc_inode+0x22/0xa0
>> > > [ 567.045045] new_inode_pseudo+0x12/0x60
>> > > [ 567.045049] new_inode+0x17/0x30
>> > > [ 567.045052] mqueue_get_inode+0x45/0x3b0
>> > > [ 567.045060] mqueue_fill_super+0x41/0x70
>> > > [ 567.045067] vfs_get_super+0x7f/0x100
>> > > [ 567.045074] get_tree_keyed+0x1d/0x20
>> > > [ 567.045080] mqueue_get_tree+0x1c/0x20
>> > > [ 567.045086] vfs_get_tree+0x2a/0xc0
>> > > [ 567.045092] fc_mount+0x13/0x50
>> > > [ 567.045099] mq_create_mount+0x92/0xe0
>> > > [ 567.045102] mq_init_ns+0x3b/0x50
>> > > [ 567.045106] copy_ipcs+0x10a/0x1b0
>> > > [ 567.045113] create_new_namespaces+0xa6/0x2b0
>> > > [ 567.045118] unshare_nsproxy_namespaces+0x5a/0xb0
>> > > [ 567.045124] ksys_unshare+0x19f/0x360
>> > > [ 567.045129] __x64_sys_unshare+0x12/0x20
>> > > [ 567.045135] do_syscall_64+0x38/0x90
>> > > [ 567.045143] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>> > >
>> > > For it, the __alloc_pages_nodemask() will first try process's targed
>> > > nodemask(unmovable node here), and there is no availabe zone, so it
>> > > goes with the NULL nodemask, and get a page in the slowpath.
>> >
>> > OK, I see your point now. I was not aware of the slab allocator not
>> > following cpusets. Sounds like a bug to me.
>>
>> SLAB and SLUB seem to not care about cpusets in the fast path.
>
> Is a fallback to a different node which is outside of the cpuset
> possible?

AFAICS anything in per-cpu cache will be allocated without looking at the
cpuset, so it can be outside of the cpuset. In SLUB slowpath, get_partial_node()
looking for fallback on the same node will also not look at cpuset.
get_any_partial() looking for a fallback allocation on any node does check
cpuset_zone_allowed() and obey it strictly. A fallback to page allocator will
obey whatever page allocator obeys.

So if a process cannot is restricted to allocate from node X via cpuset *and*
also cannot be executed on CPU's from node X via taskset, then it AFAICS
effectively cannot violate the cpuset in SLUB because it won't reach the percpu
or per-node caches that don't check cpusets.

>> But this
>> stack shows that it went all the way to the page allocator, so the cpusets
>> should have been obeyed there at least.
>
> Looking closer what is this dump_stack saying actually?

Yes, is that a dump of successful allocation (that violates cpusets?) or a
failing one?

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