* [PATCH] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT
@ 2021-12-10 2:06 Waiman Long
2021-12-10 2:47 ` Waiman Long
0 siblings, 1 reply; 2+ messages in thread
From: Waiman Long @ 2021-12-10 2:06 UTC (permalink / raw)
To: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton
Cc: linux-kernel, cgroups, linux-mm, Sebastian Andrzej Siewior,
Thomas Gleixner, Waiman Long
Direct calls to local_irq_{save/restore}() and preempt_{enable/disable}()
are not appropriate for PREEMPT_RT. To provide better PREEMPT_RT support,
change local_irq_{save/restore}() to local_lock_irq{save/restore}() and
add a local_lock_t to struct memcg_stock_pcp.
Also disable the task and interrupt context optimization for obj_stock as
there will be no performance gain in the case of PREEMPT_RT. In this case,
task obj_stock will be there but remain unused.
Signed-off-by: Waiman Long <longman@redhat.com>
---
mm/memcontrol.c | 41 ++++++++++++++++++++++-------------------
1 file changed, 22 insertions(+), 19 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6863a834ed42..c984d3054478 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2109,6 +2109,7 @@ struct obj_stock {
};
struct memcg_stock_pcp {
+ local_lock_t lock;
struct mem_cgroup *cached; /* this never be root cgroup */
unsigned int nr_pages;
struct obj_stock task_obj;
@@ -2147,29 +2148,28 @@ static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
* which is cheap in non-preempt kernel. The interrupt context object stock
* can only be accessed after disabling interrupt. User context code can
* access interrupt object stock, but not vice versa.
+ *
+ * This task and interrupt context optimization is disabled for PREEMPT_RT
+ * as there is no performance gain in this case.
*/
static inline struct obj_stock *get_obj_stock(unsigned long *pflags)
{
- struct memcg_stock_pcp *stock;
-
- if (likely(in_task())) {
+ if (likely(in_task()) && !IS_ENABLED(CONFIG_PREEMPT_RT)) {
*pflags = 0UL;
preempt_disable();
- stock = this_cpu_ptr(&memcg_stock);
- return &stock->task_obj;
+ return this_cpu_ptr(&memcg_stock.task_obj);
}
- local_irq_save(*pflags);
- stock = this_cpu_ptr(&memcg_stock);
- return &stock->irq_obj;
+ local_lock_irqsave(&memcg_stock.lock, *pflags);
+ return this_cpu_ptr(&memcg_stock.irq_obj);
}
static inline void put_obj_stock(unsigned long flags)
{
- if (likely(in_task()))
+ if (likely(in_task()) && !IS_ENABLED(CONFIG_PREEMPT_RT))
preempt_enable();
else
- local_irq_restore(flags);
+ local_unlock_irqrestore(&memcg_stock.lock, flags);
}
/**
@@ -2192,7 +2192,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
if (nr_pages > MEMCG_CHARGE_BATCH)
return ret;
- local_irq_save(flags);
+ local_lock_irqsave(&memcg_stock.lock, flags);
stock = this_cpu_ptr(&memcg_stock);
if (memcg == stock->cached && stock->nr_pages >= nr_pages) {
@@ -2200,7 +2200,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
ret = true;
}
- local_irq_restore(flags);
+ local_unlock_irqrestore(&memcg_stock.lock, flags);
return ret;
}
@@ -2236,7 +2236,7 @@ static void drain_local_stock(struct work_struct *dummy)
* drain_stock races is that we always operate on local CPU stock
* here with IRQ disabled
*/
- local_irq_save(flags);
+ local_lock_irqsave(&memcg_stock.lock, flags);
stock = this_cpu_ptr(&memcg_stock);
drain_obj_stock(&stock->irq_obj);
@@ -2245,7 +2245,7 @@ static void drain_local_stock(struct work_struct *dummy)
drain_stock(stock);
clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
- local_irq_restore(flags);
+ local_unlock_irqrestore(&memcg_stock.lock, flags);
}
/*
@@ -2257,7 +2257,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
struct memcg_stock_pcp *stock;
unsigned long flags;
- local_irq_save(flags);
+ local_lock_irqsave(&memcg_stock.lock, flags);
stock = this_cpu_ptr(&memcg_stock);
if (stock->cached != memcg) { /* reset if necessary */
@@ -2270,7 +2270,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
if (stock->nr_pages > MEMCG_CHARGE_BATCH)
drain_stock(stock);
- local_irq_restore(flags);
+ local_unlock_irqrestore(&memcg_stock.lock, flags);
}
/*
@@ -7059,9 +7059,12 @@ static int __init mem_cgroup_init(void)
cpuhp_setup_state_nocalls(CPUHP_MM_MEMCQ_DEAD, "mm/memctrl:dead", NULL,
memcg_hotplug_cpu_dead);
- for_each_possible_cpu(cpu)
- INIT_WORK(&per_cpu_ptr(&memcg_stock, cpu)->work,
- drain_local_stock);
+ for_each_possible_cpu(cpu) {
+ struct memcg_stock_pcp *stock = per_cpu_ptr(&memcg_stock, cpu);
+
+ INIT_WORK(&stock->work, drain_local_stock);
+ local_lock_init(&stock->lock);
+ }
for_each_node(node) {
struct mem_cgroup_tree_per_node *rtpn;
--
2.27.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT
2021-12-10 2:06 [PATCH] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT Waiman Long
@ 2021-12-10 2:47 ` Waiman Long
0 siblings, 0 replies; 2+ messages in thread
From: Waiman Long @ 2021-12-10 2:47 UTC (permalink / raw)
To: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton
Cc: linux-kernel, cgroups, linux-mm, Sebastian Andrzej Siewior,
Thomas Gleixner
On 12/9/21 21:06, Waiman Long wrote:
> Direct calls to local_irq_{save/restore}() and preempt_{enable/disable}()
> are not appropriate for PREEMPT_RT. To provide better PREEMPT_RT support,
> change local_irq_{save/restore}() to local_lock_irq{save/restore}() and
> add a local_lock_t to struct memcg_stock_pcp.
>
> Also disable the task and interrupt context optimization for obj_stock as
> there will be no performance gain in the case of PREEMPT_RT. In this case,
> task obj_stock will be there but remain unused.
>
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
> mm/memcontrol.c | 41 ++++++++++++++++++++++-------------------
> 1 file changed, 22 insertions(+), 19 deletions(-)
Sorry, this doesn't apply to linux-next as it conflicts with a previous
patch that I sent out. Will send out a v2 soon.
-Longman
^ permalink raw reply [flat|nested] 2+ messages in thread
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