Messages in this thread | | | Date | Fri, 28 Jan 2022 11:03:41 +0530 | From | Srikar Dronamraju <> | Subject | Re: [RFC PATCH 2/2] NUMA balancing: avoid to migrate task to CPU-less node |
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* Huang Ying <ying.huang@intel.com> [2022-01-28 10:38:42]:
> In a typical memory tiering system, there's no CPU in slow (PMEM) NUMA > nodes. But if the number of the hint page faults on a PMEM node is > the max for a task, The current NUMA balancing policy may try to place > the task on the PMEM node instead of DRAM node. This is unreasonable, > because there's no CPU in PMEM NUMA nodes. To fix this, CPU-less > nodes are ignored when searching the migration target node for a task > in this patch. > > To test the patch, we run a workload that accesses more memory in PMEM > node than memory in DRAM node. Without the patch, the PMEM node will > be chosen as preferred node in task_numa_placement(). While the DRAM > node will be chosen instead with the patch. > > Signed-off-by: "Huang, Ying" <ying.huang@intel.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Mel Gorman <mgorman@suse.de> > Cc: Rik van Riel <riel@surriel.com> > Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com> > --- > kernel/sched/fair.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 54e1aad1c5d7..e462ac5c1e48 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2393,6 +2393,10 @@ static void task_numa_placement(struct task_struct *p) > } > } > > + /* Cannot migrate task to CPU-less node */ > + if (!node_state(nid, N_CPU)) > + continue; > +
Lets take the example that you quoted 2 socket machine with 1 DRAM node and 1 PMEM node per socket. Now lets say the task is placed on a CPU in node 1 but most of its memory faults are coming from node 2, which is the PMEM node attached to node 0. Now without the hunk, there is a chance that the task got moved to node 0. However with the change, are we inhibiting such a move?
> if (!ng) { > if (faults > max_faults) { > max_faults = faults; > -- > 2.30.2 >
-- Thanks and Regards Srikar Dronamraju
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