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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
