On Tue, Oct 16, 2012 at 06:25:06PM +0000, Christoph Lameter wrote:

On Tue, 16 Oct 2012, Glauber Costa wrote:

quoted

+ memory.kmem.limit_in_bytes      # set/show hard limit for kernel memory
+ memory.kmem.usage_in_bytes      # show current kernel memory allocation
+ memory.kmem.failcnt             # show the number of kernel memory usage hits limits
+ memory.kmem.max_usage_in_bytes  # show max kernel memory usage recorded

Does it actually make sense to limit kernel memory? The user generally has
no idea how much kernel memory a process is using and kernel changes can
change the memory footprint. Given the fuzzy accounting in the kernel a
large cache refill (if someone configures the slab batch count to be
really big f.e.) can account a lot of memory to the wrong cgroup. The
allocation could fail.

Limiting the total memory use of a process (U+K) would make more sense I
guess. Only U is probably sufficient? In what way would a limitation on
kernel memory in use be good?

It's about preventing abuses caused by bugs or malicious use and avoiding
groups stepping on each others' toes. You're saying that letting a group
to allocate 32GB of paged memory is the same as 32GB of kernel memory?

I don't belive sysadmins will keep a tight limit for kernel memory but rather
a safety limit in case something goes wrong. usage_in_bytes will provide
data to get the limits better adjusted.

The innacuracy of the kmem accounting is (AFAIK) a cost tradeoff.

--
Aristeu