kernel-packages team mailing list archive

[Tim Gardner <tim.gardner@xxxxxxxxxxxxx>]

Documentation/cgroups/memory.txt:

2.7 Kernel Memory Extension (CONFIG_MEMCG_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 won't be accounted at all until limit on a group is set. This
allows for existing setups to continue working without disruption.  The limit
cannot be set if the cgroup have children, or if there are already tasks in the
cgroup. Attempting to set the limit under those conditions will return -EBUSY.
When use_hierarchy == 1 and a group is accounted, its children will
automatically be accounted regardless of their limit value.

After a group is first limited, it will be kept being accounted until it
is removed. The memory limitation itself, can of course be removed by writing
-1 to memory.kmem.limit_in_bytes. In this case, kmem will be accounted, but not
limited.

Kernel memory limits are not imposed for the root cgroup. Usage for the root
cgroup may or may not be accounted. The memory used is accumulated into
memory.kmem.usage_in_bytes, or in a separate counter when it makes sense.
(currently only for tcp).
The main "kmem" counter is fed into the main counter, so kmem charges will
also be visible from the user counter.

Currently no soft limit is implemented for kernel memory. It is future work
to trigger slab reclaim when those limits are reached.


** Also affects: linux (Ubuntu Trusty)
   Importance: Undecided
       Status: New

** Changed in: linux (Ubuntu Trusty)
       Status: New => In Progress

** Changed in: linux (Ubuntu Trusty)
     Assignee: (unassigned) => Tim Gardner (timg-tpi)

-- 
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/1309586

Title:
  enable CONFIG_MEMCG_KMEM

Status in “linux” package in Ubuntu:
  In Progress
Status in “linux” source package in Trusty:
  In Progress

Bug description:
  CONFIG_MEMCG_KMEM is disabled in the trusty kernel.  It's the
  recommended way to prevent forkbombs, so if there's not a good reason
  to have it disabled, it would be great if that could be changed.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1309586/+subscriptions