From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: cgroups@vger.kernel.org, linux-mm@kvack.org
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Johannes Weiner" <hannes@cmpxchg.org>,
"Michal Hocko" <mhocko@kernel.org>,
"Michal Koutný" <mkoutny@suse.com>,
"Peter Zijlstra" <peterz@infradead.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Vladimir Davydov" <vdavydov.dev@gmail.com>,
"Waiman Long" <longman@redhat.com>,
"Sebastian Andrzej Siewior" <bigeasy@linutronix.de>
Subject: [PATCH v2 3/4] mm/memcg: Protect per-CPU counter by disabling preemption on PREEMPT_RT where needed.
Date: Fri, 11 Feb 2022 23:35:36 +0100 [thread overview]
Message-ID: <20220211223537.2175879-4-bigeasy@linutronix.de> (raw)
In-Reply-To: <20220211223537.2175879-1-bigeasy@linutronix.de>
The per-CPU counter are modified with the non-atomic modifier. The
consistency is ensured by disabling interrupts for the update.
On non PREEMPT_RT configuration this works because acquiring a
spinlock_t typed lock with the _irq() suffix disables interrupts. On
PREEMPT_RT configurations the RMW operation can be interrupted.
Another problem is that mem_cgroup_swapout() expects to be invoked with
disabled interrupts because the caller has to acquire a spinlock_t which
is acquired with disabled interrupts. Since spinlock_t never disables
interrupts on PREEMPT_RT the interrupts are never disabled at this
point.
The code is never called from in_irq() context on PREEMPT_RT therefore
disabling preemption during the update is sufficient on PREEMPT_RT.
The sections which explicitly disable interrupts can remain on
PREEMPT_RT because the sections remain short and they don't involve
sleeping locks (memcg_check_events() is doing nothing on PREEMPT_RT).
Disable preemption during update of the per-CPU variables which do not
explicitly disable interrupts.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
mm/memcontrol.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c1caa662946dc..466466f285cea 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -705,6 +705,8 @@ void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
memcg = pn->memcg;
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_disable();
/* Update memcg */
__this_cpu_add(memcg->vmstats_percpu->state[idx], val);
@@ -712,6 +714,8 @@ void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
__this_cpu_add(pn->lruvec_stats_percpu->state[idx], val);
memcg_rstat_updated(memcg, val);
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_enable();
}
/**
@@ -794,8 +798,12 @@ void __count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx,
if (mem_cgroup_disabled())
return;
+ if (IS_ENABLED(PREEMPT_RT))
+ preempt_disable();
__this_cpu_add(memcg->vmstats_percpu->events[idx], count);
memcg_rstat_updated(memcg, count);
+ if (IS_ENABLED(PREEMPT_RT))
+ preempt_enable();
}
static unsigned long memcg_events(struct mem_cgroup *memcg, int event)
@@ -7148,9 +7156,18 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
* i_pages lock which is taken with interrupts-off. It is
* important here to have the interrupts disabled because it is the
* only synchronisation we have for updating the per-CPU variables.
+ * On PREEMPT_RT interrupts are never disabled and the updates to per-CPU
+ * variables are synchronised by keeping preemption disabled.
*/
- VM_BUG_ON(!irqs_disabled());
- mem_cgroup_charge_statistics(memcg, -nr_entries);
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+ VM_BUG_ON(!irqs_disabled());
+ mem_cgroup_charge_statistics(memcg, -nr_entries);
+ } else {
+ preempt_disable();
+ mem_cgroup_charge_statistics(memcg, -nr_entries);
+ preempt_enable();
+ }
+
memcg_check_events(memcg, page_to_nid(page));
css_put(&memcg->css);
--
2.34.1
next prev parent reply other threads:[~2022-02-11 22:35 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-11 22:35 [PATCH v2 0/4] mm/memcg: Address PREEMPT_RT problems instead of disabling it Sebastian Andrzej Siewior
2022-02-11 22:35 ` [PATCH v2 1/4] mm/memcg: Revert ("mm/memcg: optimize user context object stock access") Sebastian Andrzej Siewior
2022-02-14 16:23 ` Johannes Weiner
2022-02-14 19:45 ` Roman Gushchin
2022-02-11 22:35 ` [PATCH v2 2/4] mm/memcg: Disable threshold event handlers on PREEMPT_RT Sebastian Andrzej Siewior
2022-02-14 16:23 ` Johannes Weiner
2022-02-14 19:46 ` Roman Gushchin
2022-02-11 22:35 ` Sebastian Andrzej Siewior [this message]
2022-02-14 16:46 ` [PATCH v2 3/4] mm/memcg: Protect per-CPU counter by disabling preemption on PREEMPT_RT where needed Johannes Weiner
2022-02-14 19:53 ` Roman Gushchin
2022-02-15 18:01 ` Sebastian Andrzej Siewior
2022-02-11 22:35 ` [PATCH v2 4/4] mm/memcg: Protect memcg_stock with a local_lock_t Sebastian Andrzej Siewior
2022-02-14 16:23 ` Johannes Weiner
2022-02-16 15:51 ` Sebastian Andrzej Siewior
2022-02-16 18:08 ` Johannes Weiner
2022-02-17 9:28 ` Sebastian Andrzej Siewior
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