[RFC 00/18] Present useful limits to user

[Topi Miettinen]

Hello,

There are many basic ways to control processes, including capabilities,
cgroups and resource limits. However, there are far fewer ways to find out
useful values for the limits, except blind trial and error.

This patch series attempts to fix that by giving at least a nice starting
point from the actual maximum values. I looked where each limit is checked
and added a call to limit bump nearby.


Capabilities
[RFC 01/18] capabilities: track actually used capabilities

Currently, there is no way to know which capabilities are actually used. Even
the source code is only implicit, in-depth knowledge of each capability must
be used when analyzing a program to judge which capabilities the program will
exercise.
 
Cgroups
[RFC 02/18] cgroup_pids: track maximum pids
[RFC 03/18] memcontrol: present maximum used memory also for
[RFC 04/18] device_cgroup: track and present accessed devices

For tasks and memory cgroup limits the situation is somewhat better as the
current tasks and memory status can be easily seen with ps(1). However, any
transient tasks or temporary higher memory use might slip from the view.
Device use may be seen with advanced MAC tools, like TOMOYO, but there is no
universal method. Program sources typically give no useful indication about
memory use or how many tasks there could be.
 
Resource limits
[RFC 05/18] limits: track and present RLIMIT_NOFILE actual max
[RFC 06/18] limits: present RLIMIT_CPU and RLIMIT_RTTIMER current
[RFC 07/18] limits: track RLIMIT_FSIZE actual max
[RFC 08/18] limits: track RLIMIT_DATA actual max
[RFC 09/18] limits: track RLIMIT_CORE actual max
[RFC 10/18] limits: track RLIMIT_STACK actual max
[RFC 11/18] limits: track and present RLIMIT_NPROC actual max
[RFC 12/18] limits: track RLIMIT_MEMLOCK actual max
[RFC 13/18] limits: track RLIMIT_AS actual max
[RFC 14/18] limits: track RLIMIT_SIGPENDING actual max
[RFC 15/18] limits: track RLIMIT_MSGQUEUE actual max
[RFC 16/18] limits: track RLIMIT_NICE actual max
[RFC 17/18] limits: track RLIMIT_RTPRIO actual max
[RFC 18/18] proc: present VM_LOCKED memory in /proc/self/maps

Current number of files and current VM usage (data pages, address space size)
could be calculated from available /proc files. Again, any temporarily higher
values could be easily missed. For many limits, there is no way to see what
is the current situation and source code is mostly useless.

As a side note, the resouce limits seem to be in bad shape. For example,
RLIMIT_MEMLOCK is used incoherently and I think VM statistics can miss
some changes. Adding RLIMIT_CODE could be useful.

The current maximum values for the resource limits are now shown in
/proc/task/limits. If this is deemed too confusing for the existing
programs which rely on the exact format, I can change that to a new file.


Finally, the patches work in my testing but I have probably missed finer
lock/RCU details.

-Topi