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SubjectRe: The performance and behaviour of the anti-fragmentation related patches
Andrew Morton wrote:
> So some urgent questions are: how are we going to do mem hotunplug and
> per-container RSS?
> Our basic unit of memory management is the zone. Right now, a zone maps
> onto some hardware-imposed thing. But the zone-based MM works *well*. I
> suspect that a good way to solve both per-container RSS and mem hotunplug
> is to split the zone concept away from its hardware limitations: create a
> "software zone" and a "hardware zone". All the existing page allocator and
> reclaim code remains basically unchanged, and it operates on "software
> zones". Each software zones always lies within a single hardware zone.
> The software zones are resizeable. For per-container RSS we give each
> container one (or perhaps multiple) resizeable software zones.
> For memory hotunplug, some of the hardware zone's software zones are marked
> reclaimable and some are not; DIMMs which are wholly within reclaimable
> zones can be depopulated and powered off or removed.
> NUMA and cpusets screwed up: they've gone and used nodes as their basic
> unit of memory management whereas they should have used zones. This will
> need to be untangled.
> Anyway, that's just a shot in the dark. Could be that we implement unplug
> and RSS control by totally different means. But I do wish that we'd sort
> out what those means will be before we potentially complicate the story a
> lot by adding antifragmentation.

Paul Menage had suggested something very similar in response to the RFC
for memory controllers I sent out and it was suggested that we create
small zones (roughly 64 MB) to avoid the issue of a zone/node not being
a shareable across containers. Even with a small size, there are some
issues. The following thread has the details discussed.

RSS accounting is very easy (with minimal changes to the core mm),
supplemented with an efficient per-container reclaimer, it should be
easy to implement a good per-container RSS controller.

Warm Regards,
Balbir Singh
Linux Technology Center
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