Re: [mm/migrate] 9eeb73028c: stress-ng.memhotplug.ops_per_sec -53.8% regression

Oliver Sang
2021-10-21T14:11:53Z

hi, All,

we confirmed this regression was fixed by
commit: 295be91f7ef0027fca2f2e4788e99731aa931834 ("mm/migrate: optimize hotplug-time demotion order updates")
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master

the report link is:
https://lists.01.org/hyperkitty/list/lkp@lists.01.org/thread/4KKRZ7CSIPKMD3Q43GZTGQXA6WBJM2XO/

On Fri, Sep 17, 2021 at 11:14:59AM +0800, Huang, Ying wrote:
> Hi, Oliver,
>
> kernel test robot <oliver.sang@intel.com> writes:
>
> > Greeting,
> >
> > FYI, we noticed a -53.8% regression of stress-ng.memhotplug.ops_per_sec due to commit:
> >
> >
> > commit: 9eeb73028cfb54eb06efe87c50cc014d3f1ff43e ("[patch 174/212] mm/migrate: update node demotion order on hotplug events")
> > url: https://github.com/0day-ci/linux/commits/Andrew-Morton/ia64-fix-typo-in-a-comment/20210903-065028
> >
> >
> > in testcase: stress-ng
> > on test machine: 96 threads 2 sockets Intel(R) Xeon(R) Gold 6252 CPU @ 2.10GHz with 192G memory
> > with following parameters:
> >
> > nr_threads: 10%
> > disk: 1HDD
> > testtime: 60s
> > fs: ext4
> > class: os
> > test: memhotplug
> > cpufreq_governor: performance
> > ucode: 0x5003006
> >
>
> Can you help to test whether the following patch can recover the
> regression?
>
> Best Regards,
> Huang, Ying
>
> ----------------------------8<--------------------------------------
> From 5d3e18a9f083954584932a20233ef489d9398342 Mon Sep 17 00:00:00 2001
> From: Huang Ying <ying.huang@intel.com>
> Date: Thu, 16 Sep 2021 16:51:44 +0800
> Subject: [PATCH] mm/migrate: recover hotplug performance regression
>
> 0-Day kernel test robot reported a -53.8% performance regression for
> stress-ng memhotplug test case. This patch is to recover the
> regression via avoid updating the demotion order if not necessary.
>
> Refer: https://lore.kernel.org/lkml/20210905135932.GE15026@xsang-OptiPlex-9020/
> Fixes: 884a6e5d1f93 ("mm/migrate: update node demotion order on hotplug events")
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Cc: Yang Shi <shy828301@gmail.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Wei Xu <weixugc@google.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Greg Thelen <gthelen@google.com>
> Cc: Keith Busch <kbusch@kernel.org>
> ---
> mm/migrate.c | 26 ++++++++++++++++++++++----
> 1 file changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 77d107a4577f..20d803707497 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1145,6 +1145,8 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> static int node_demotion[MAX_NUMNODES] __read_mostly =
> {[0 ... MAX_NUMNODES - 1] = NUMA_NO_NODE};
>
> +static bool node_demotion_disabled __read_mostly;
> +
> /**
> * next_demotion_node() - Get the next node in the demotion path
> * @node: The starting node to lookup the next node
> @@ -1158,6 +1160,8 @@ int next_demotion_node(int node)
> {
> int target;
>
> + if (node_demotion_disabled)
> + return NUMA_NO_NODE;
> /*
> * node_demotion[] is updated without excluding this
> * function from running. RCU doesn't provide any
> @@ -3198,13 +3202,26 @@ static void __set_migration_target_nodes(void)
> goto again;
> }
>
> +static int nr_node_has_cpu;
> +static int nr_node_has_mem;
> +
> +static void check_set_migration_target_nodes(void)
> +{
> + if (num_node_state(N_MEMORY) != nr_node_has_mem ||
> + num_node_state(N_CPU) != nr_node_has_cpu) {
> + __set_migration_target_nodes();
> + nr_node_has_mem = num_node_state(N_MEMORY);
> + nr_node_has_cpu = num_node_state(N_CPU);
> + }
> +}
> +
> /*
> * For callers that do not hold get_online_mems() already.
> */
> static void set_migration_target_nodes(void)
> {
> get_online_mems();
> - __set_migration_target_nodes();
> + check_set_migration_target_nodes();
> put_online_mems();
> }
>
> @@ -3249,7 +3266,7 @@ static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
> * will leave migration disabled until the offline
> * completes and the MEM_OFFLINE case below runs.
> */
> - disable_all_migrate_targets();
> + node_demotion_disabled = true;
> break;
> case MEM_OFFLINE:
> case MEM_ONLINE:
> @@ -3257,14 +3274,15 @@ static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
> * Recalculate the target nodes once the node
> * reaches its final state (online or offline).
> */
> - __set_migration_target_nodes();
> + check_set_migration_target_nodes();
> + node_demotion_disabled = false;
> break;
> case MEM_CANCEL_OFFLINE:
> /*
> * MEM_GOING_OFFLINE disabled all the migration
> * targets. Reenable them.
> */
> - __set_migration_target_nodes();
> + node_demotion_disabled = false;
> break;
> case MEM_GOING_ONLINE:
> case MEM_CANCEL_ONLINE:
> --
> 2.30.2
>