Re: [RFC PATCH 0/2] mm: fix OOMs for binding workloads to movable zone only node

[Michal Hocko]

On Thu 05-11-20 21:43:05, Feng Tang wrote:
> On Thu, Nov 05, 2020 at 02:12:45PM +0100, Michal Hocko wrote:
> > On Thu 05-11-20 21:07:10, Feng Tang wrote:
> > [...]
> > > My debug traces shows it is, and its gfp_mask is 'GFP_KERNEL'
> > 
> > Can you provide the full information please? Which node has been
> > requested. Which cpuset the calling process run in and which node has
> > the allocation succeeded from? A bare dump_stack without any further
> > context is not really helpful.
> 
> I don't have the same platform as the original report, so I simulated
> one similar setup (with fakenuma and movablecore), which has 2 memory
> nodes: node 0 has DMA0/DMA32/Movable zones, while node 1 has only
> Movable zone. With it, I can got the same error and same oom callstack
> as the original report (as in the cover-letter).
> 
> The test command is:
> 	# docker run -it --rm --cpuset-mems 1 ubuntu:latest bash -c "grep Mems_allowed /proc/self/status"
> 
> To debug I only added some trace in the __alloc_pages_nodemask(), and
> for the callstack which get the page successfully:
> 
> 	[  567.510903] Call Trace:
> 	[  567.510909]  dump_stack+0x74/0x9a
> 	[  567.510910]  __alloc_pages_nodemask.cold+0x22/0xe5
> 	[  567.510913]  alloc_pages_current+0x87/0xe0
> 	[  567.510914]  __vmalloc_node_range+0x14c/0x240
> 	[  567.510918]  module_alloc+0x82/0xe0
> 	[  567.510921]  bpf_jit_alloc_exec+0xe/0x10
> 	[  567.510922]  bpf_jit_binary_alloc+0x7a/0x120
> 	[  567.510925]  bpf_int_jit_compile+0x145/0x424
> 	[  567.510926]  bpf_prog_select_runtime+0xac/0x130

As already said this doesn't really tell much without the additional
information.

> The incomming parameter nodemask is NULL, and the function will first try the
> cpuset nodemask (1 here), and the zoneidx is only granted 2, which makes the
> 'ac's preferred zone to be NULL. so it goes into __alloc_pages_slowpath(),
> which will first set the nodemask to 'NULL', and this time it got a preferred
> zone: zone DMA32 from node 0, following get_page_from_freelist will allocate
> one page from that zone. 

I do not follow. Both hot and slow paths of the allocator set
ALLOC_CPUSET or emulate it by mems_allowed when cpusets are nebaled
IIRC. This is later enforced in get_page_from_free_list. There are some
exceptions when the allocating process can run away from its cpusets -
e.g. IRQs, OOM victims and few other cases but definitely not a random
allocation. There might be some subtle details that have changed or I
might have forgot but 
-- 
Michal Hocko
SUSE Labs