Messages in this thread |  | | | Date | Thu, 21 Jan 2010 14:09:48 +0000 | | From | Mel Gorman <> | | Subject | Re: [PATCH 5/7] Add /proc trigger for memory compaction |
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On Wed, Jan 20, 2010 at 12:48:05PM -0800, David Rientjes wrote: > On Wed, 20 Jan 2010, Mel Gorman wrote: > > > > With Lee's work on mempolicy-constrained hugepage allocations, there is a > > > use-case for this explicit trigger to be exported via sysfs in the > > > longterm: > > > > True, although the per-node structures are only available on NUMA making > > it necessary to have two interfaces. The per-node one is handy enough > > because it would be just > > > > /sys/devices/system/node/nodeX/compact_node > > When written to, this node is compacted by the writing process > > > > But there does not appear to be a "good" way of having a non-NUMA > > interface. /sys/devices/system/node does not exist .... Does anyone > > remember why !NUMA does not have a /sys/devices/system/node/node0? Is > > there a good reason or was there just no point? > > > > There doesn't seem to be a usecase for a fake node0 sysfs entry since it > would be a duplication of procfs. >
Indeed.
> I think it would be best to create a global /proc/sys/vm/compact trigger > that would walk all "compactable" zones system-wide
Easily done.
> and then a per-node > /sys/devices/system/node/nodeX/compact trigger for that particular node, > both with permissions 0200. >
Will work on this as an additional patch. It should be straight-forward with the only care needing to be taken around memory hotplug as usual.
> It would be helpful to be able to determine what is "compactable" at the > same time by adding both global and per-node "compact_order" tunables that > would default to HUGETLB_PAGE_ORDER.
Well, rather than having a separate tunable, writing a number to /proc/sys/vm/compact could indicate the order if that trigger is now working system-wide. Would that be suitable?
> Then, the corresponding "compact" > trigger would only do work if fill_contig_page_info() shows > !free_blocks_suitable for either all zones (global trigger) or each zone > in the node's zonelist (per-node trigger). >
Do you see a need for proc to act like this? I'm wondering if try_to_compact_pages() already does what you're looking for except no process is required to muck around in /proc or /sys.
I somewhat saw the /proc and /sys tunables being used for either debugging or by a job scheduler that compacted one or more nodes before a new job started.
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
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