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Date: Tue, 26 Jul 2022 16:02:33 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org,
Wei Xu <weixugc@...gle.com>, Yang Shi <shy828301@...il.com>,
Davidlohr Bueso <dave@...olabs.net>,
Tim C Chen <tim.c.chen@...el.com>,
Michal Hocko <mhocko@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Hesham Almatary <hesham.almatary@...wei.com>,
Dave Hansen <dave.hansen@...el.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Alistair Popple <apopple@...dia.com>,
Dan Williams <dan.j.williams@...el.com>,
Johannes Weiner <hannes@...xchg.org>, jvgediya.oss@...il.com
Subject: Re: [PATCH v10 6/8] mm/demotion: Add pg_data_t member to track node
memory tier details
"Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> writes:
> Also update different helpes to use NODE_DATA()->memtier. Since
> node specific memtier can change based on the reassignment of
> NUMA node to a different memory tiers, accessing NODE_DATA()->memtier
> needs to happen under an rcu read lock or memory_tier_lock.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> ---
> include/linux/mmzone.h | 3 ++
> mm/memory-tiers.c | 65 +++++++++++++++++++++++++++++++++++-------
> 2 files changed, 57 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index aab70355d64f..353812495a70 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -928,6 +928,9 @@ typedef struct pglist_data {
> /* Per-node vmstats */
> struct per_cpu_nodestat __percpu *per_cpu_nodestats;
> atomic_long_t vm_stat[NR_VM_NODE_STAT_ITEMS];
> +#ifdef CONFIG_NUMA
> + struct memory_tier __rcu *memtier;
> +#endif
> } pg_data_t;
>
> #define node_present_pages(nid) (NODE_DATA(nid)->node_present_pages)
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index a8cfe2ca3903..4715f9b96a44 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -138,13 +138,18 @@ static struct memory_tier *find_create_memory_tier(unsigned int perf_level)
>
> static struct memory_tier *__node_get_memory_tier(int node)
> {
> - struct memory_tier *memtier;
> + pg_data_t *pgdat;
>
> - list_for_each_entry(memtier, &memory_tiers, list) {
> - if (node_isset(node, memtier->nodelist))
> - return memtier;
> - }
> - return NULL;
> + pgdat = NODE_DATA(node);
> + if (!pgdat)
> + return NULL;
> + /*
> + * Since we hold memory_tier_lock, we can avoid
> + * RCU read locks when accessing the details. No
> + * parallel updates are possible here.
> + */
> + return rcu_dereference_check(pgdat->memtier,
> + lockdep_is_held(&memory_tier_lock));
> }
>
> #ifdef CONFIG_MIGRATION
> @@ -277,6 +282,29 @@ static inline void disable_all_migrate_targets(void) {}
> static inline void establish_migration_targets(void) {}
> #endif /* CONFIG_MIGRATION */
>
> +static void memtier_node_set(int node, struct memory_tier *memtier)
> +{
> + pg_data_t *pgdat;
> + struct memory_tier *current_memtier;
> +
> + pgdat = NODE_DATA(node);
> + if (!pgdat)
> + return;
> + /*
> + * Make sure we mark the memtier NULL before we assign the new memory tier
> + * to the NUMA node. This make sure that anybody looking at NODE_DATA
> + * finds a NULL memtier or the one which is still valid.
> + */
> + current_memtier = rcu_dereference_check(pgdat->memtier,
> + lockdep_is_held(&memory_tier_lock));
> + rcu_assign_pointer(pgdat->memtier, NULL);
> + synchronize_rcu();
> + if (current_memtier)
> + node_clear(node, current_memtier->nodelist);
If pgdat->memtier == NULL, we don't need to set it to NULL and call
synchronize_rcu(). That is,
+ current_memtier = rcu_dereference_check(pgdat->memtier,
+ lockdep_is_held(&memory_tier_lock));
+ if (current_memtier) {
+ rcu_assign_pointer(pgdat->memtier, NULL);
+ synchronize_rcu();
+ node_clear(node, current_memtier->nodelist);
+ }
Same for clear_node_memory_tier().
Best Regards,
Huang, Ying
> + node_set(node, memtier->nodelist);
> + rcu_assign_pointer(pgdat->memtier, memtier);
> +}
> +
> static void init_node_memory_tier(int node)
> {
> int perf_level;
> @@ -295,7 +323,7 @@ static void init_node_memory_tier(int node)
> if (!memtier) {
> perf_level = node_devices[node]->perf_level;
> memtier = find_create_memory_tier(perf_level);
> - node_set(node, memtier->nodelist);
> + memtier_node_set(node, memtier);
> }
> establish_migration_targets();
> mutex_unlock(&memory_tier_lock);
> @@ -303,12 +331,25 @@ static void init_node_memory_tier(int node)
>
> static void clear_node_memory_tier(int node)
> {
> - struct memory_tier *memtier;
> + pg_data_t *pgdat;
> + struct memory_tier *current_memtier;
> +
> + pgdat = NODE_DATA(node);
> + if (!pgdat)
> + return;
>
> mutex_lock(&memory_tier_lock);
> - memtier = __node_get_memory_tier(node);
> - if (memtier) {
> - node_clear(node, memtier->nodelist);
> + /*
> + * Make sure we mark the memtier NULL before we assign the new memory tier
> + * to the NUMA node. This make sure that anybody looking at NODE_DATA
> + * finds a NULL memtier or the one which is still valid.
> + */
> + current_memtier = rcu_dereference_check(pgdat->memtier,
> + lockdep_is_held(&memory_tier_lock));
> + rcu_assign_pointer(pgdat->memtier, NULL);
> + synchronize_rcu();
> + if (current_memtier) {
> + node_clear(node, current_memtier->nodelist);
> establish_migration_targets();
> }
> mutex_unlock(&memory_tier_lock);
> @@ -383,6 +424,8 @@ static int __init memory_tier_init(void)
>
> if (!node_property->perf_level)
> node_property->perf_level = default_memtier_perf_level;
> +
> + rcu_assign_pointer(NODE_DATA(node)->memtier, memtier);
> }
> mutex_unlock(&memory_tier_lock);
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