Re: [PATCH v5 0/8] per-cgroup tcp buffer pressure settings

On Tue,  4 Oct 2011 16:17:52 +0400
Glauber Costa [off-list ref] wrote:

[[ v3: merge Kirill's suggestions, + a destroy-related bugfix ]]
[[ v4: Fix a bug with non-mounted cgroups + disallow task movement ]]
[[ v5: Compile bug with modular ipv6 + tcp files in bytes ]]

Kame, Kirill,

I am submitting this again merging most of your comments. I've decided to
leave some of them out:
 * I am not using res_counters for allocated_memory. Besides being more
   expensive than what we need, to make it work in a nice way, we'd have
   to change the !cgroup code, including other protocols than tcp. Also,
   
 * I am not using failcnt and max_usage_in_bytes for it. I believe the value
   of those lies more in the allocation than in the pressure control. Besides,
   fail conditions lie mostly outside of the memory cgroup's control. (Actually,
   a soft_limit makes a lot of sense, and I do plan to introduce it in a follow
   up series)

If you agree with the above, and there are any other pressing issues, let me
know and I will address them ASAP. Otherwise, let's discuss it. I'm always open.

I'm not familar with reuqirements of users. So, I appreciate your choices.
What I adivse you here is taking a deep breath. Making new version every day
is not good for reviewing process ;)
(It's now -rc8 and merge will not be so quick, anyway.)

At this stage, my concern is view of interfaces and documenation, and future plans.

Let me give  a try explanation by myself. (Correct me ;)
I added some questions but I'm sorry you've already answered.

New interfaces are 5 files. All files exists only for non-root memory cgroup.

1. memory.independent_kmem_limit
2. memory.kmem.usage_in_bytes
3. memory.kmem.limit_in_bytes
4. memory.kmem.tcp.limit_in_bytes
5. memory.kmem.tcp.usage_in_bytes

* memory.independent_kmem_limit
 If 1, kmem_limit_in_bytes/kmem_usage_in_bytes works.
 If 0, kmem_limit_in_bytes/kmem_usage_in_bytes doesn't work and all kmem
    usages are controlled under memory.limit_in_bytes.

Question:
 - What happens when parent/chidlren cgroup has different indepedent_kmem_limit ?
 - What happens at creating a new cgroup with use_hierarchy==1.

* memory.kmem_limit_in_bytes/memory.kmem.tcp.limit_in_bytes

 Both files works independently for _Now_. And memory.kmem_usage_in_bytes and
 memory.kmem_tcp.usage_in_bytes has no relationships.

 In future plan, kmem.usage_in_bytes should includes tcp.kmem_usage_in_bytes.
 And kmem.limit_in_bytes should be the limiation of sum of all kmem.xxxx.limit_in_bytes.

Question:
 - Why this integration is difficult ?
   Can't tcp-limit-code borrows some amount of charges in batch from kmem_limit 
   and use it ?
 
 - Don't you need a stat file to indicate "tcp memory pressure works!" ?
   It can be obtained already ?

Thanks,
-Kame

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