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 X-OriginatorOrg: oracle.com X-MS-Exchange-CrossTenant-Network-Message-Id: 27640efd-b5bf-467b-3461-08dd81ebebee X-MS-Exchange-CrossTenant-AuthSource: PH7PR10MB5747.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Apr 2025 22:20:43.5014 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 2yLPkiwKtgxAcZ7L5uBD4xsBuVWGD+IisVrK6qxjBIxdXHebJfNRqPcj4xPGV+iK4npKs9XmBmUBYI48F6lzDQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR10MB6957 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1095,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-04-22_10,2025-04-22_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 mlxscore=0 adultscore=0 phishscore=0 mlxlogscore=999 bulkscore=0 malwarescore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2504070000 definitions=main-2504220168 X-Proofpoint-GUID: U0J9RCIMyN4acx5gxyY79KyFIgsyLQfs X-Proofpoint-ORIG-GUID: U0J9RCIMyN4acx5gxyY79KyFIgsyLQfs X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNDIyMDE2OCBTYWx0ZWRfX2IrjGCu+Xqt7 s4SgXtSIek3hdl4igOlhI1/LezLjeIi2Gfw5rSbbRNcAggu3G3uvvh5vYPJnps0phSNFRx6tIbJ UolO1J9BitdRFcONwmy2OjSL0fMV/vpY9op0fY1Js2zeyC4rStcIqM6PyHFNiINu7zv+JQriJV1 5IE4lzZ0vpxlwov+sl465aKFOT6fjfFb/pFgZyuBPUi5wWiOHsEzWbSHD98iZ062+ybpPdrlV9K xq3cBhcaZ9L51b+/zApriigcflSVGLsshT9t+qNqHINYYD6kYyOdlmurIlo16HbpznwGKKHVxFr BCrVsifq3zTMoqoVb6SVuXqxPNT+/lU8KpJ31cmxnDY+kT6KWv/CV9Cl6wWpSjuuVyOmgBCQ+pl UHHbqzxE Hi Yu On 4/19/25 04:16, Chen, Yu C wrote: > Hi Libo, > > On 4/18/2025 3:15 AM, Libo Chen wrote: >> When the memory of the current task is pinned to one NUMA node by cgroup, >> there is no point in continuing the rest of VMA scanning and hinting page >> faults as they will just be overhead. With this change, there will be no >> more unnecessary PTE updates or page faults in this scenario. >> >> We have seen up to a 6x improvement on a typical java workload running on >> VMs with memory and CPU pinned to one NUMA node via cpuset in a two-socket >> AARCH64 system. With the same pinning, on a 18-cores-per-socket Intel >> platform, we have seen 20% improvment in a microbench that creates a >> 30-vCPU selftest KVM guest with 4GB memory, where each vCPU reads 4KB >> pages in a fixed number of loops. >> >> Signed-off-by: Libo Chen > > I think this is a promising change that we can perform fine-grain NUMA > balance control on a per-cgroup basis rather than system-wide NUMA > balance for every task, which is costly. > Yes indeed, the cost, from we have seen, can be quite astonishing >> --- >>   kernel/sched/fair.c | 7 +++++++ >>   1 file changed, 7 insertions(+) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index e43993a4e5807..c9903b1b39487 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -3329,6 +3329,13 @@ static void task_numa_work(struct callback_head *work) >>       if (p->flags & PF_EXITING) >>           return; >>   +    /* >> +     * Memory is pinned to only one NUMA node via cpuset.mems, naturally >> +     * no page can be migrated. >> +     */ >> +    if (cpusets_enabled() && nodes_weight(cpuset_current_mems_allowed) == 1) >> +        return; >> + > > I found that you had a proposal in V1 to address Peter's concern[1]: > Allow the task to be migrated to its preferred Node, even if the task's > memory policy is restricted to 1 Node. In your previous proposal, only if the task's cpumask is bound to the same Node as its memory policy node, the NUMA balance scanning is skipped, because a cgroup usually binds its tasks and memory allocation policy to the same node. Not sure if that could be turned into: > > If the task's memory policy node's CPU mask is a subset of the task's cpumask, the NUMA balance scan is allowed. > I guess fundamentally is this really worth it? Do the benefits of NUMA task migrations only outweigh the overheads of VMA scanning, PTE updates and page faults etc? I suppose this is workload-dependent, but what about the best-case scenario? I think we probably need more data. Also if we do that, we also need to do the same for other VMA skipping scenarios. Thanks, Libo > For example, > Suppose p's memory is only allocated on node0, which contains CPU2, CPU3. > 1. If p's CPU affinity is CPU0, CPU1, there is no need to do NUMA balancing scanning, because CPU0,1 are not in p's legitimate cpumask. > 2. If p's CPU affinity is CPU3, there is no need to do NUMA balancing scanning. p is already on its preferred node. > 3. But if p's CPU affinity is CPU2, CPU3, CPU6, the NUMA balancing scan should be allowed. Because it is possible to migrate p from CPU6 to either CPU2 or CPU3. > > What I'm thinking of is something as follows(untested): > if (cpusets_enabled() && >     nodes_weight(cpuset_current_mems_allowed) == 1 && >     !cpumask_subset(cpumask_of_node(cpuset_current_mems_allowed), >             p->cpus_ptr)) >     return; > > > I tested your patch on top of the latest sched/core, > binding task CPU affinity to Node1 and memory allocation node on > Node1: > echo "8-15" > /sys/fs/cgroup/mytest/cpuset.cpus > echo "1" > /sys/fs/cgroup/mytest/cpuset.mems > cgexec -g cpuset:mytest ./run-mmtests.sh --no-monitor --config config-numa skip_scan > > And it works as expected: > # bpftrace numa_trace.bt > > @sched_skip_cpuset_numa: 133 > > > thanks, > Chenyu > > [1] https://urldefense.com/v3/__https://lore.kernel.org/lkml/cde7af54-5481-499e-8a42-0111f555f2b1@oracle.com/__;!!ACWV5N9M2RV99hQ!OvO0A__dCkeSB4eze2TYZYDHWGg0ubi04-u8lW5NCQGRE6vZkCGahdWMzHtpKMMDSt-L1wCkM8ILMIP3YA$ > >>       if (!mm->numa_next_scan) { >>           mm->numa_next_scan = now + >>               msecs_to_jiffies(sysctl_numa_balancing_scan_delay);