Messages in this thread | | | Date | Mon, 4 Dec 2006 11:41:42 -0800 (PST) | From | Christoph Lameter <> | Subject | Re: [PATCH] Add __GFP_MOVABLE for callers to flag allocations that may be migrated |
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On Mon, 4 Dec 2006, Andrew Morton wrote:
> My concern is that __GFP_MOVABLE is useful for fragmentation-avoidance, but > useless for memory hot-unplug. So that if/when hot-unplug comes along > we'll add more gunk which is a somewhat-superset of the GFP_MOVABLE > infrastructure, hence we didn't need the GFP_MOVABLE code. Or something.
It is useless for memory unplug until we implement limits for unmovable pages in a zone (per MA_ORDER area? That would fit nicely into the anti frag scheme) or until we have logic that makes !GFP_MOVABLE allocations fall back to a node that is not removable.
> That depends on how we do hot-unplug, if we do it. I continue to suspect > that it'll be done via memory zones: effectively by resurrecting > GFP_HIGHMEM. In which case there's little overlap with anti-frag. (btw, I > have a suspicion that the most important application of memory hot-unplug > will be power management: destructively turning off DIMMs).
There are numerous other uses as well (besides DIMM and node unplug):
1. Faulty DIMM isolation 2. Virtual memory managers can reduce memory without resorting to balloons. 3. Physical removal and exchange of memory while a system is running (Likely necessary to complement hotplug cpu, cpus usually come with memory).
The multi zone approach does not work with NUMA. NUMA only supports a single zone for memory policy control etc. Also multiple zones carry with it a management overhead that is unnecessary for the MOVABLE/UNMOVABLE distinction.
> perhaps not for the hugetlbpage problem. Whereas anti-fragmentation adds > vastly more code, but can address both problems? Or something.
I'd favor adding full defragmentation. - 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/
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