On 5/25/19 8:28 PM, Andrew Morton wrote:
> (Cc Vlastimil)
Oh dear, 2 years and I forgot all the details about how this works.
> On Sat, 25 May 2019 15:07:23 +0800 zhong jiang <zhongjiang@xxxxxxxxxx> wrote:
>
>> We bind an different node to different vma, Unluckily,
>> it will bind different vma to same node by checking the /proc/pid/numa_maps.
>> Commit 213980c0f23b ("mm, mempolicy: simplify rebinding mempolicies when updating cpusets")
>> has introduced the issue. when we change memory policy by seting cpuset.mems,
>> A process will rebind the specified policy more than one times.
>> if the cpuset_mems_allowed is not equal to user specified nodes. hence the issue will trigger.
>> Maybe result in the out of memory which allocating memory from same node.
I have a hard time understanding what the problem is. Could you please
write it as a (pseudo) reproducer? I.e. an example of the process/admin
mempolicy/cpuset actions that have some wrong observed results vs the
correct expected result.
>> --- a/mm/mempolicy.c
>> +++ b/mm/mempolicy.c
>> @@ -345,7 +345,7 @@ static void mpol_rebind_nodemask(struct mempolicy *pol, const nodemask_t *nodes)
>> else {
>> nodes_remap(tmp, pol->v.nodes,pol->w.cpuset_mems_allowed,
>> *nodes);
>> - pol->w.cpuset_mems_allowed = tmp;
>> + pol->w.cpuset_mems_allowed = *nodes;
Looks like a mechanical error on my side when removing the code for
step1+step2 rebinding. Before my commit there was
pol->w.cpuset_mems_allowed = step ? tmp : *nodes;
Since 'step' was removed and thus 0, I should have used *nodes indeed.
Thanks for catching that.
>> }
>>
>> if (nodes_empty(tmp))
>
> hm, I'm not surprised the code broke. What the heck is going on in
> there? It used to have a perfunctory comment, but Vlastimil deleted
> it.
Yeah the comment was specific for the case that was being removed.
> Could someone please propose a comment for the above code block
> explaining why we're doing what we do?
I'll have to relearn this first...
