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Subject[RFC][PATCH 0/4] Memory controller soft limit patches

Here is v1 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. We'll compare shares and soft limits
below. I've had soft limit implementations earlier, but I've discarded those
approaches in favour of this one.

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.

This is an RFC implementation and is not meant for inclusion


1. The shares interface is not yet implemented, the current soft limit
implementation is not yet hierarchy aware. The end goal is to add
a shares interface on top of soft limits and to maintain shares in
a manner similar to the group scheduler
2. The current implementation maintains the delta from the soft limit
and pushes back groups to their soft limits, a ratio of delta/soft_limit
is more useful
3. It would be nice to have more targetted reclaim (in terms of pages to
recalim) interface. So that groups are pushed back, close to their soft


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.

Please review, comment.




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