On Mon, Nov 24, 2014 at 01:33:42PM -0800, David Rientjes wrote: > On Mon, 24 Nov 2014, Kirill A. Shutemov wrote: > > > > This make sure that we try to allocate hugepages from local node. If > > > we can't we fallback to small page allocation based on > > > mempolicy. This is based on the observation that allocating pages > > > on local node is more beneficial that allocating hugepages on remote node. > > > > Local node on allocation is not necessary local node for use. > > If policy says to use a specific node[s], we should follow. > > > > True, and the interaction between thp and mempolicies is fragile: if a > process has a MPOL_BIND mempolicy over a set of nodes, that does not > necessarily mean that we want to allocate thp remotely if it will always > be accessed remotely. It's simple to benchmark and show that remote > access latency of a hugepage can exceed that of local pages. MPOL_BIND > itself is a policy of exclusion, not inclusion, and it's difficult to > define when local pages and its cost of allocation is better than remote > thp. > > For MPOL_BIND, if the local node is allowed then thp should be forced from > that node, if the local node is disallowed then allocate from any node in > the nodemask. For MPOL_INTERLEAVE, I think we should only allocate thp > from the next node in order, otherwise fail the allocation and fallback to > small pages. Is this what you meant as well? Correct. > > I think it makes sense to force local allocation if policy is interleave > > or if current node is in preferred or bind set. > > > > If local allocation were forced for MPOL_INTERLEAVE and all memory is > initially faulted by cpus on a single node, then the policy has > effectively become MPOL_DEFAULT, there's no interleave. You're right. I don't have much experience with mempolicy code. -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>