Messages in this thread | | | Date | Thu, 1 Mar 2007 19:05:48 -0800 (PST) | From | Christoph Lameter <> | Subject | Re: The performance and behaviour of the anti-fragmentation related patches |
| |
On Thu, 1 Mar 2007, Andrew Morton wrote:
> What worries me is memory hot-unplug and per-container RSS limits. We > don't know how we're going to do either of these yet, and it could well be > that the anti-frag work significantly complexicates whatever we end up > doing there.
Right now it seems that the per container RSS limits differ from the statistics calculated per zone. There would be a conceptual overlap but the containers are optional and track numbers differently. There is no RSS counter in a zone f.e.
memory hot-unplug would directly tap into the anti-frag work. Essentially only the zone with movable pages would be unpluggable without additional measures. Making slab items and other allocations that is fixed movable requires work anyways. A new zone concept will not help.
> For prioritisation purposes I'd judge that memory hot-unplug is of similar > value to the antifrag work (because memory hot-unplug permits DIMM > poweroff).
I would say that anti-frag / defrag enables memory unplug.
> And I'd judge that per-container RSS limits are of considerably more value > than antifrag (in fact per-container RSS might be a superset of antifrag, > in the sense that per-container RSS and containers could be abused to fix > the i-cant-get-any-hugepages problem, dunno).
They relate? How can a container perform antifrag? Meaning a container reserves a portion of a hardware zone and becomes a software zone.
> So some urgent questions are: how are we going to do mem hotunplug and > per-container RSS?
Separately. There is no need to mingle these two together.
> 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
Thats a value judgement that I doubt. Zone based balancing is bad and has been repeatedly patched up so that it works with the usual loads.
> 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.
Resizable software zones? Are they contiguous or not? If not then we add another layer to the defrag problem.
> 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.
So subzones indeed. How about calling the MAX_ORDER entities that Mel's patches create "software zones"?
> 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.
zones have hardware characteristics at its core. In a NUMA setting zones determine the performance of loads from those areas. I would like to have zones and nodes merged. Maybe extend node numbers into the negative area -1 = DMA -2 DMA32 etc? All systems then manage the "nones" (node / zones meerged). One could create additional "virtual" nones after the real nones that have hardware characteristics behind them. The virtual nones would be something like the software zones? Contain MAX_ORDER portions of hardware nones?
> 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.
Hmmm.... My shot:
1. Merge zones/nodes
2. Create new virtual zones/nodes that are subsets of MAX_order blocks of the real zones/nodes. These may then have additional characteristics such as
A. moveable/unmovable B. DMA restrictions C. container assignment.
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |