On Mon 05-09-22 18:30:55, Zhongkun He wrote:
Hi Michal, thanks for your reply.
The current 'mempolicy' is hierarchically independent. The default value of
the child is to inherit from the parent. The modification of the child
policy will not be restricted by the parent.
This breaks cgroup fundamental property of hierarchical enforcement of
each property. And as such it is a no go.
Of course, there are other options, such as the child's policy mode must be
the same as the parent's. node can be the subset of parent's, but the
interleave type will be complicated, that's why hierarchy independence is
used. It would be better if you have other suggestions?
Honestly, I am not really sure cgroup cpusets is a great fit for this
usecase. It would be probably better to elaborate some more what are the
existing shortcomings and what you would like to achieve. Just stating
the syscall is a hard to use interface is not quite clear on its own.
Btw. have you noticed this question?
What is the hierarchical behavior of the policy? Say parent has a
stronger requirement (say bind) than a child (prefer)?
How to use the mempolicy interface:
echo prefer:2 > /sys/fs/cgroup/zz/cpuset.mems.policy
echo bind:1-3 > /sys/fs/cgroup/zz/cpuset.mems.policy
echo interleave:0,1,2,3 >/sys/fs/cgroup/zz/cpuset.mems.policy
Am I just confused or did you really mean to combine all these
together?
Hi Michal, thanks for your reply.
>>Say parent has a stronger requirement (say bind) than a child(prefer)?
Yes, combine all these together. The parent's task will use 'bind',
child's use 'prefer'.This is the current implementation, and we can
discuss and modify it together if there are other suggestions.
1:Existing shortcomings
In our use case, the application and the control plane are two separate
systems. When the application is created, it doesn't know how to use
memory, and it doesn't care. The control plane will decide the memory
usage policy based on different reasons (the attributes of the
application itself, the priority, the remaining resources of the
system). Currently, numactl is used to set it at program startup, and
the child process will inherit the mempolicy. But we can't dynamically
adjust the memory policy, except restart, the memory policy will not change.
2:Our goals
For the above reasons, we want to create a mempolicy at the cgroup
level. Usually processes under a cgroup have the same priority and
attributes, and we can dynamically adjust the memory allocation strategy
according to the remaining resources of the system. For example, a
low-priority cgroup uses the 'bind:2-3' policy, and a high-priority
cgroup uses bind:0-1. When resources are insufficient, it will be
changed to bind:3, bind:0-2 by control plane, etc.Further more, more
mempolicy can be extended, such as allocating memory according to node
weight, etc.
Thanks.
