On 2022-02-14 11:23:11 [-0500], Johannes Weiner wrote:
> Hi Sebastian,
Hi Johannes,
> This is a bit dubious in terms of layering. It's an objcg operation,
> but what's "locked" isn't the objcg, it's the underlying stock. That
> function then looks it up again, even though we have it right there.
>
> You can open-code it and factor out the stock operation instead, and
> it makes things much simpler and clearer.
>
> I.e. something like this (untested!):
This then:
------>8------
From: Johannes Weiner <hannes@xxxxxxxxxxx>
Date: Wed, 16 Feb 2022 13:25:49 +0100
Subject: [PATCH] mm/memcg: Opencode the inner part of
obj_cgroup_uncharge_pages() in drain_obj_stock()
Provide the inner part of refill_stock() as __refill_stock() without
disabling interrupts. This eases the integration of local_lock_t where
recursive locking must be avoided.
Open code obj_cgroup_uncharge_pages() in drain_obj_stock() and use
__refill_stock(). The caller of drain_obj_stock() already disables
interrupts.
[bigeasy: Patch body around Johannes' diff ]
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
mm/memcontrol.c | 25 +++++++++++++++++++------
1 file changed, 19 insertions(+), 6 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 69130a5fe3d51..f574f2e1cc399 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2227,12 +2227,9 @@ static void drain_local_stock(struct work_struct *dummy)
* Cache charges(val) to local per_cpu area.
* This will be consumed by consume_stock() function, later.
*/
-static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
+static void __refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
{
struct memcg_stock_pcp *stock;
- unsigned long flags;
-
- local_irq_save(flags);
stock = this_cpu_ptr(&memcg_stock);
if (stock->cached != memcg) { /* reset if necessary */
@@ -2244,7 +2241,14 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
if (stock->nr_pages > MEMCG_CHARGE_BATCH)
drain_stock(stock);
+}
+static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
+{
+ unsigned long flags;
+
+ local_irq_save(flags);
+ __refill_stock(memcg, nr_pages);
local_irq_restore(flags);
}
@@ -3151,8 +3155,17 @@ static void drain_obj_stock(struct memcg_stock_pcp *stock)
unsigned int nr_pages = stock->nr_bytes >> PAGE_SHIFT;
unsigned int nr_bytes = stock->nr_bytes & (PAGE_SIZE - 1);
- if (nr_pages)
- obj_cgroup_uncharge_pages(old, nr_pages);
+ if (nr_pages) {
+ struct mem_cgroup *memcg;
+
+ memcg = get_mem_cgroup_from_objcg(old);
+
+ if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
+ page_counter_uncharge(&memcg->kmem, nr_pages);
+ __refill_stock(memcg, nr_pages);
+
+ css_put(&memcg->css);
+ }
/*
* The leftover is flushed to the centralized per-memcg value.
--
2.34.1
