[PATCH 0/5] Memory controller soft limit patches (v7)

[Balbir Singh <balbir@linux.vnet.ibm.com>]

From: Balbir Singh <balbir@linux.vnet.ibm.com>

New Feature: Soft limits for memory resource controller.

Changelog v7...v6
1. Added checks in reclaim path to make sure we don't infinitely loop
2. Refactored reclaim options into a new patch
3. Tested several scenarios, see tests below

Changelog v6...v5
1. If the number of reclaimed pages are zero, select the next mem cgroup
   for reclamation
2. Fixed a bug, where key was being updated after insertion into the tree
3. Fixed a build issue, when CONFIG_MEM_RES_CTLR is not enabled

Changelog v5...v4
1. Several changes to the reclaim logic, please see the patch 4 (reclaim on
   contention). I've experimented with several possibilities for reclaim
   and chose to come back to this due to the excellent behaviour seen while
   testing the patchset.
2. Reduced the overhead of soft limits on resource counters very significantly.
   Reaim benchmark now shows almost no drop in performance.

Changelog v4...v3
1. Adopted suggestions from Kamezawa to do a per-zone-per-node reclaim
   while doing soft limit reclaim. We don't record priorities while
   doing soft reclaim
2. Some of the overheads associated with soft limits (like calculating
   excess each time) is eliminated
3. The time_after(jiffies, 0) bug has been fixed
4. Tasks are throttled if the mem cgroup they belong to is being soft reclaimed
   and at the same time tasks are increasing the memory footprint and causing
   the mem cgroup to exceed its soft limit.

Changelog v3...v2
1. Implemented several review comments from Kosaki-San and Kamezawa-San
   Please see individual changelogs for changes

Changelog v2...v1
1. Soft limits now support hierarchies
2. Use spinlocks instead of mutexes for synchronization of the RB tree

Here is v7 of the new soft limit implementation. Soft limits is a new feature
for the memory resource controller, something similar has existed in the
group scheduler in the form of shares. The CPU controllers interpretation
of shares is very different though. 

Soft limits are the most useful feature to have for environments where
the administrator wants to overcommit the system, such that only on memory
contention do the limits become active. The current soft limits implementation
provides a soft_limit_in_bytes interface for the memory controller and not
for memory+swap controller. The implementation maintains an RB-Tree of groups
that exceed their soft limit and starts reclaiming from the group that
exceeds this limit by the maximum amount.

So far I have the best test results with this patchset. I've experimented with
several approaches and methods. I might be a little delayed in responding,
I might have intermittent access to the internet for the next few days.

TODOs

1. The current implementation maintains the delta from the soft limit
   and pushes back groups to their soft limits, a ratio of delta/soft_limit
   might be more useful


Tests
-----

I've run two memory intensive workloads with differing soft limits and
seen that they are pushed back to their soft limit on contention. Their usage
was their soft limit plus additional memory that they were able to grab
on the system. Soft limit can take a while before we see the expected
results.

The other tests I've run are
1. Deletion of groups while soft limit is in progress in the hierarchy
2. Setting the soft limit to zero and running other groups with non-zero
   soft limits.
3. Setting the soft limit to zero and testing if the mem cgroup is able
   to use available memory
4. Tested the patches with hierarchy enabled
5. Tested with swapoff -a, to make sure we don't go into an infinite loop

Please review, comment.

Series
------


memcg-soft-limits-documentation.patch
memcg-soft-limits-interface.patch
memcg-soft-limits-organize.patch
memcg-soft-limits-refactor-reclaim-bits
memcg-soft-limits-reclaim-on-contention.patch


-- 
	Balbir

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>