Re: [PATCH v6 01/10] Basic kernel memory functionality for the MemoryController

[Glauber Costa]

On 11/28/2011 12:24 AM, KAMEZAWA Hiroyuki wrote:
> On Fri, 25 Nov 2011 15:38:07 -0200
> Glauber Costa<glommer@xxxxxxxxxxxxx>  wrote:
>
> > This patch lays down the foundation for the kernel memory component
> > of the Memory Controller.
> >
> > As of today, I am only laying down the following files:
> >
> >   * memory.independent_kmem_limit
> >   * memory.kmem.limit_in_bytes (currently ignored)
> >   * memory.kmem.usage_in_bytes (always zero)
> >
> > Signed-off-by: Glauber Costa<glommer@xxxxxxxxxxxxx>
> > Reviewed-by: Kirill A. Shutemov<kirill@xxxxxxxxxxxxx>
> > CC: Paul Menage<paul@xxxxxxxxxxxxxx>
> > CC: Greg Thelen<gthelen@xxxxxxxxxx>
> > ---
> >   Documentation/cgroups/memory.txt |   36 ++++++++++++-
> >   init/Kconfig                     |   14 +++++
> >   mm/memcontrol.c                  |  107 ++++++++++++++++++++++++++++++++++++--
> >   3 files changed, 150 insertions(+), 7 deletions(-)
> >
> > diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> > index 06eb6d9..bf00cd2 100644
> > --- a/Documentation/cgroups/memory.txt
> > +++ b/Documentation/cgroups/memory.txt
> > @@ -44,8 +44,9 @@ Features:
> >    - oom-killer disable knob and oom-notifier
> >    - Root cgroup has no limit controls.
> >
> > - Kernel memory and Hugepages are not under control yet. We just manage
> > - pages on LRU. To add more controls, we have to take care of performance.
> > + Hugepages is not under control yet. We just manage pages on LRU. To add more
> > + controls, we have to take care of performance. Kernel memory support is work
> > + in progress, and the current version provides basically functionality.
> >
> >   Brief summary of control files.
> >
> > @@ -56,8 +57,11 @@ Brief summary of control files.
> >   				 (See 5.5 for details)
> >    memory.memsw.usage_in_bytes	 # show current res_counter usage for memory+Swap
> >   				 (See 5.5 for details)
> > + memory.kmem.usage_in_bytes	 # show current res_counter usage for kmem only.
> > +				 (See 2.7 for details)
> >    memory.limit_in_bytes		 # set/show limit of memory usage
> >    memory.memsw.limit_in_bytes	 # set/show limit of memory+Swap usage
> > + memory.kmem.limit_in_bytes	 # if allowed, set/show limit of kernel memory
> >    memory.failcnt			 # show the number of memory usage hits limits
> >    memory.memsw.failcnt		 # show the number of memory+Swap hits limits
> >    memory.max_usage_in_bytes	 # show max memory usage recorded
> > @@ -72,6 +76,9 @@ Brief summary of control files.
> >    memory.oom_control		 # set/show oom controls.
> >    memory.numa_stat		 # show the number of memory usage per numa node
> >
> > + memory.independent_kmem_limit	 # select whether or not kernel memory limits are
> > +				   independent of user limits
> > +
> >   1. History
> >
> >   The memory controller has a long history. A request for comments for the memory
> > @@ -255,6 +262,31 @@ When oom event notifier is registered, event will be delivered.
> >     per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by
> >     zone->lru_lock, it has no lock of its own.
> >
> > +2.7 Kernel Memory Extension (CONFIG_CGROUP_MEM_RES_CTLR_KMEM)
> > +
> > + With the Kernel memory extension, the Memory Controller is able to limit
> > +the amount of kernel memory used by the system. Kernel memory is fundamentally
> > +different than user memory, since it can't be swapped out, which makes it
> > +possible to DoS the system by consuming too much of this precious resource.
> > +Kernel memory limits are not imposed for the root cgroup.
> > +
> > +Memory limits as specified by the standard Memory Controller may or may not
> > +take kernel memory into consideration. This is achieved through the file
> > +memory.independent_kmem_limit. A Value different than 0 will allow for kernel
> > +memory to be controlled separately.
> > +
> > +When kernel memory limits are not independent, the limit values set in
> > +memory.kmem files are ignored.
> > +
> > +Currently no soft limit is implemented for kernel memory. It is future work
> > +to trigger slab reclaim when those limits are reached.
> > +
> > +CAUTION: As of this writing, the kmem extention may prevent tasks from moving
> > +among cgroups. If a task has kmem accounting in a cgroup, the task cannot be
> > +moved until the kmem resource is released. Also, until the resource is fully
> > +released, the cgroup cannot be destroyed. So, please consider your use cases
> > +and set kmem extention config option carefully.
> > +
>
> This seems that memcg 'has' kernel memory limiting feature for all kinds of kmem..
> Could you add a list of "currently controled kmems" section ?
> And update the list in later patch ?
>
> Thanks,
> -Kame
Hi Kame,

Thanks for your review.
Since none of your comments are blockers, I'd prefer to send follow up 
patches if you don't mind - assuming Dave won't have any restrictions 
himself that would prevent him from picking this series. If I have to 
resend it anyway, I'll be more than happy to address them all in my next 
submission


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