[Devel] Re: [RFC][PATCH 0/3] Kernel memory accounting container (v2)

[Balbir Singh]

Pavel Emelyanov wrote:
> Long time ago we decided to start memory control with the
> user memory container. Now this container in -mm tree and
> I think we can start with (at least discussion of) the
> kmem one.
> 
> Changes from v.1:
> * fixed Paul's comment about subsystem registration
> * return ERR_PTR from ->create callback, not NULL
> * make container-to-object assignment in rcu-safe section
> * make turning accounting on and off with "1" and "0"
> 
> ============================================================
> 
> First of all - why do we need this kind of control. The major
> "pros" is that kernel memory control protects the system
> from DoS attacks by processes that live in container. As our
> experience shows many exploits simply do not work in the
> container with limited kernel memory.
> 
> I can split the kernel memory container into 4 parts:
> 
> 1. kmalloc-ed objects control
> 2. vmalloc-ed objects control
> 3. buddy allocated pages control
> 4. kmem_cache_alloc-ed objects control
> 
> the control of first tree types of objects has one peculiarity:
> one need to explicitly point out which allocations he wants to
> account and this becomes not-configurable and is to be discussed.
> 
> On the other hands such objects as anon_vma-s, file-s, sighangds,
> vfsmounts, etc are created by user request always and should
> always be accounted. Fortunately they are allocated from their
> own caches and thus the whole kmem cache can be accountable.
> 
> This is exactly what this patchset does - it adds the ability
> to account for the total size of kmem-cache-allocated objects
> from specified kmem caches.
> 
> This is based on the SLUB allocator, Paul's containers and the
> resource counters I made for RSS controller and which are in
> -mm tree already.
> 

Does this mean that the kernel memory container will have a dependency
on SLUB and it will be disabled for SLAB and SLOB allocators?
SLAB is going to go away soon anyway and I guess not too many
people use SLOB.

> To play with it, one need to mount the container file system
> with -o kmem and then mark some caches as accountable via
> /sys/slab/<cache_name>/cache_account.
> 
> As I have already told kmalloc caches cannot be accounted easily
> so turning the accounting on for them will fail with -EINVAL.
> Turning the accounting off is possible only if the cache has
> no objects. This is done so because turning accounting off
> implies unaccounting of all the objects in the cache, but due
> to full-pages in slub are not stored in any lists (usually)
> this is impossible to do so, however I'm open for discussion
> of how to make this work.
> 

I remember discussing with you, but I can't remember the rational,
could you please explain it again.

> I know it's maybe too late, since some of you may be preparing
> for the Summit or LinixConf, but I think that we can go on
> discussing these on LinuxConf.
> 

The LinuxConf and kernel summit is done now :-)

> The patches are applicable to the latest Morton's tree (that
> without the RSS controll) with the resource counters patch
> Andrew committed recently.
> 

This is a bit confusing, it is applicable to 2.6.23-rc4-mm1?

> I've made some minimal testing for that and the similar code
> (without the containers interface but with the kmalloc 
> accounting) is already in our 2.6.22 OpenVZ tree, so testing
> is going on.
> 
> Thanks,
> Pavel


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL