Re: [next -v1 4/5] memcg: factor out the __refill_obj_stock function

[Chen Ridong]

On 2024/12/18 2:19, Shakeel Butt wrote:
> On Fri, Dec 06, 2024 at 01:35:11AM +0000, Chen Ridong wrote:
>> From: Chen Ridong <chenridong@xxxxxxxxxx>
>>
>> Factor out the '__refill_obj_stock' function to make the code more
>> cohesive.
>>
>> Signed-off-by: Chen Ridong <chenridong@xxxxxxxxxx>
>> ---
>>  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.
> 

Thank you for your review。

How about keeping the check in the calling functions and renaming like that:
/* Replace the stock objcg with objcg, return the old objcg */
static obj_cgroup *replace_stock_objcg (struct memcg_stock_pcp *stock,
struct obj_cgroup *objcg)

Best regards,
Ridong

>> +		*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
>>