On Thu 05-11-20 09:40:28, Feng Tang wrote: > On Wed, Nov 04, 2020 at 09:53:43AM +0100, Michal Hocko wrote: > > > > > As I've said in reply to your second patch. I think we can make the oom > > > > killer behavior more sensible in this misconfigured cases but I do not > > > > think we want break the cpuset isolation for such a configuration. > > > > > > Do you mean we skip the killing and just let the allocation fail? We've > > > checked the oom killer code first, when the oom happens, both DRAM > > > node and unmovable node have lots of free memory, and killing process > > > won't improve the situation. > > > > We already do skip oom killer and fail for lowmem allocation requests already. > > This is similar in some sense. Another option would be to kill the > > allocating context which will have less corner cases potentially because > > some allocation failures might be unexpected. > > Yes, this can avoid the helpless oom killing to kill a good process(no > memory pressure at all) > > And I think the important thing is to judge whether this usage (binding > docker like workload to unmovable node) is a valid case :) I am confused. Why wouldbe an unmovable node a problem. Movable allocations can be satisfied from the Zone Normal just fine. It is other way around that is a problem. > Initially, I thought it invalid too, but later think it still makes some > sense for the 2 cases: > * user want to bind his workload to one node(most of user space > memory) to avoid cross-node traffic, and that node happens to > be configured as unmovable See above > * one small DRAM node + big PMEM node, and memory latency insensitive > workload could be bound to the cheaper unmovable PMEM node Please elaborate some more. As long as you have movable and normal nodes then this should be possible with a deal of care - most notably the movable:kernel ratio memory shouldn't be too big. Besides that why does PMEM node have to be MOVABLE only in the first place? > > > (Folloing is copied from your comments for 2/2) > > > > This allows to spill memory allocations over to any other node which > > > > has Normal (or other lower) zones and as such it breaks cpuset isolation. > > > > As I've pointed out in the reply to your cover letter it seems that > > > > this is more of a misconfiguration than a bug. > > > > > > For the usage case (docker container running), the spilling is already > > > happening, I traced its memory allocation requests, many of them are > > > movable, and got fallback to the normal node naturally with current > > > > 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. -- Michal Hocko SUSE Labs
