Commit 200577f6 authored by Shakeel Butt's avatar Shakeel Butt Committed by Andrew Morton
Browse files

memcg: objcg stock trylock without irq disabling 

There is no need to disable irqs to use objcg per-cpu stock, so let's just
not do that but consume_obj_stock() and refill_obj_stock() will need to
use trylock instead to avoid deadlock against irq.  One consequence of
this change is that the charge request from irq context may take slowpath
more often but it should be rare.

Link: https://lkml.kernel.org/r/20250514184158.3471331-8-shakeel.butt@linux.dev


Signed-off-by: default avatarShakeel Butt <shakeel.butt@linux.dev>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 0ccf1806

mm/memcontrol.c

+15 −10
Original line number Diff line number Diff line
@@ -1880,18 +1880,17 @@ static void drain_local_memcg_stock(struct work_struct *dummy) 
static void drain_local_obj_stock(struct work_struct *dummy)

{

	struct obj_stock_pcp *stock;

	unsigned long flags;



	if (WARN_ONCE(!in_task(), "drain in non-task context"))

		return;



	local_lock_irqsave(&obj_stock.lock, flags);

	local_lock(&obj_stock.lock);



	stock = this_cpu_ptr(&obj_stock);

	drain_obj_stock(stock);

	clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);



	local_unlock_irqrestore(&obj_stock.lock, flags);

	local_unlock(&obj_stock.lock);

}



static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
@@ -2874,10 +2873,10 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, 
			      struct pglist_data *pgdat, enum node_stat_item idx)

{

	struct obj_stock_pcp *stock;

	unsigned long flags;

	bool ret = false;



	local_lock_irqsave(&obj_stock.lock, flags);

	if (!local_trylock(&obj_stock.lock))

		return ret;



	stock = this_cpu_ptr(&obj_stock);

	if (objcg == READ_ONCE(stock->cached_objcg) && stock->nr_bytes >= nr_bytes) {
@@ -2888,7 +2887,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, 
			__account_obj_stock(objcg, stock, nr_bytes, pgdat, idx);

	}



	local_unlock_irqrestore(&obj_stock.lock, flags);

	local_unlock(&obj_stock.lock);



	return ret;

}
@@ -2977,10 +2976,16 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, 
		enum node_stat_item idx)

{

	struct obj_stock_pcp *stock;

	unsigned long flags;

	unsigned int nr_pages = 0;



	local_lock_irqsave(&obj_stock.lock, flags);

	if (!local_trylock(&obj_stock.lock)) {

		if (pgdat)

			mod_objcg_mlstate(objcg, pgdat, idx, nr_bytes);

		nr_pages = nr_bytes >> PAGE_SHIFT;

		nr_bytes = nr_bytes & (PAGE_SIZE - 1);

		atomic_add(nr_bytes, &objcg->nr_charged_bytes);

		goto out;

	}



	stock = this_cpu_ptr(&obj_stock);

	if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */
@@ -3002,8 +3007,8 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, 
		stock->nr_bytes &= (PAGE_SIZE - 1);

	}



	local_unlock_irqrestore(&obj_stock.lock, flags);



	local_unlock(&obj_stock.lock);

out:

	if (nr_pages)

		obj_cgroup_uncharge_pages(objcg, nr_pages);

}