linux-kernel - Re: [next -v1 4/5] memcg: factor out the __refill_obj

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Message-ID: <q7k5vqzeit4ib6joowtib6mlpwu2zdnrzse5kx44wx7jhmb6ta@w6deef6omz3d>
Date: Tue, 17 Dec 2024 10:19:38 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: akpm@...ux-foundation.org, mhocko@...nel.org, hannes@...xchg.org, 
	yosryahmed@...gle.com, roman.gushchin@...ux.dev, muchun.song@...ux.dev, 
	davidf@...eo.com, vbabka@...e.cz, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	cgroups@...r.kernel.org, chenridong@...wei.com, wangweiyang2@...wei.com
Subject: Re: [next -v1 4/5] memcg: factor out the __refill_obj_stock function

On Fri, Dec 06, 2024 at 01:35:11AM +0000, Chen Ridong wrote:
> From: Chen Ridong <chenridong@...wei.com>
> 
> Factor out the '__refill_obj_stock' function to make the code more
> cohesive.
> 
> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
>  mm/memcontrol.c | 31 ++++++++++++++++++-------------
>  1 file changed, 18 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f977e0be1c04..0c9331d7b606 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2697,6 +2697,21 @@ void __memcg_kmem_uncharge_page(struct page *page, int order)
>  	obj_cgroup_put(objcg);
>  }
>  
> +/* If the cached_objcg was refilled, return true; otherwise, return false */
> +static bool __refill_obj_stock(struct memcg_stock_pcp *stock,
> +		struct obj_cgroup *objcg, struct obj_cgroup **old_objcg)
> +{
> +	if (READ_ONCE(stock->cached_objcg) != objcg) {

Keep the above check in the calling functions and make this a void
function. Also I think we need a better name.

> +		*old_objcg = drain_obj_stock(stock);
> +		obj_cgroup_get(objcg);
> +		stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes)
> +				? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0;
> +		WRITE_ONCE(stock->cached_objcg, objcg);
> +		return true;
> +	}
> +	return false;
> +}
> +
>  static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
>  		     enum node_stat_item idx, int nr)
>  {
> @@ -2713,12 +2728,7 @@ static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
>  	 * accumulating over a page of vmstat data or when pgdat or idx
>  	 * changes.
>  	 */
> -	if (READ_ONCE(stock->cached_objcg) != objcg) {
> -		old = drain_obj_stock(stock);
> -		obj_cgroup_get(objcg);
> -		stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes)
> -				? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0;
> -		WRITE_ONCE(stock->cached_objcg, objcg);
> +	if (__refill_obj_stock(stock, objcg, &old)) {
>  		stock->cached_pgdat = pgdat;
>  	} else if (stock->cached_pgdat != pgdat) {
>  		/* Flush the existing cached vmstat data */
> @@ -2871,14 +2881,9 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
>  	local_lock_irqsave(&memcg_stock.stock_lock, flags);
>  
>  	stock = this_cpu_ptr(&memcg_stock);
> -	if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */
> -		old = drain_obj_stock(stock);
> -		obj_cgroup_get(objcg);
> -		WRITE_ONCE(stock->cached_objcg, objcg);
> -		stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes)
> -				? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0;
> +	if (__refill_obj_stock(stock, objcg, &old))
>  		allow_uncharge = true;	/* Allow uncharge when objcg changes */
> -	}
> +
>  	stock->nr_bytes += nr_bytes;
>  
>  	if (allow_uncharge && (stock->nr_bytes > PAGE_SIZE)) {
> -- 
> 2.34.1
>