[Devel] Re: [PATCH v6 01/10] Basic kernel memory functionality for the Memory Controller

[KAMEZAWA Hiroyuki]

On Mon, 28 Nov 2011 09:03:09 -0200
Glauber Costa <glommer at parallels.com> wrote:

> On 11/28/2011 12:24 AM, KAMEZAWA Hiroyuki wrote:
> > On Fri, 25 Nov 2011 15:38:07 -0200
> > Glauber Costa<glommer at parallels.com>  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 at parallels.com>
> >> Reviewed-by: Kirill A. Shutemov<kirill at shutemov.name>
> >> CC: Paul Menage<paul at paulmenage.org>
> >> CC: Greg Thelen<gthelen at google.com>
> >> ---
> >>   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
> 

As you like. But please clarify my comment which pointed out bugs in patch 02/10
and 06/10 aren't correct.

Thanks,
-Kame