Messages in this thread | | | Subject | Re: [06/44] numa: fix slab_node(MPOL_BIND) | From | Lee Schermerhorn <> | Date | Wed, 08 Dec 2010 08:53:09 -0500 |
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On Wed, 2010-12-08 at 05:33 +0100, Eric Dumazet wrote: > Le mardi 07 décembre 2010 à 22:03 -0500, Lee Schermerhorn a écrit : > > On Tue, 2010-12-07 at 16:04 -0800, Greg KH wrote: > > > 2.6.27-stable review patch. If anyone has any objections, please let us know. > > > > > > ------------------ > > > > > > From: Eric Dumazet <eric.dumazet@gmail.com> > > > > > > commit 800416f799e0723635ac2d720ad4449917a1481c upstream. > > > > > > > > > > --- a/mm/mempolicy.c > > > +++ b/mm/mempolicy.c > > > @@ -1404,7 +1404,7 @@ unsigned slab_node(struct mempolicy *pol > > > (void)first_zones_zonelist(zonelist, highest_zoneidx, > > > &policy->v.nodes, > > > &zone); > > > - return zone->node; > > > + return zone ? zone->node : numa_node_id(); > > > > I think this should be numa_mem_id(). Given the documented purpose of > > slab_node(), we want a node from which page allocation is likely to > > succeed. numa_node_id() can return a memoryless node for, e.g., some > > configurations of some HP ia64 platforms. numa_mem_id() was introduced > > to return that same node from which "local" mempolicy would allocate > > pages. > > Hmm... numa_mem_id() was introduced in 2.6.35 as an optimization. > > When I did this patch (to fix a bug), mm/mempolicy.c only contained > calls to numa_node_id() (and still is today)
Sometimes you want numa_node_id()--e.g., for use with a mempolicy-based allocation that allows fallback. When the node id will be used for a '_THIS_NODE allocation, numa_mem_id() is preferred as it will always return a node that contains or contained--maybe now oom--memory. It's the same as numa_node_id() on platforms that don't expose memoryless nodes.
> > By the way, anybody knows how I can emulate a memoryless node on a dual > node x86_64 machine (with memory present on both nodes) ? >
You can use the mem= boot parameter and specify the amount of memory on the 1st/boot node. Or you can use the memmap parameter to reserve the memory on the 2nd/non-boot node. With the memmap parameter, you can reserve the memory of nodes other than the highest numbered one[s]--e.g., on a >2 node platform. However, you'll probably a patch to see the cpus on any node that you hide using memmap. I have such a patch if you're interested in going that route.
You can also reduce the amount of memory on any/each node by reserving ranges of physical memory with memmap. Use the 'SRAT.*PXM' boot messages to find the nodes' physical memory ranges and reserve how ever much you want off the top of the nodes.
Lee
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