Re: [PATCH] mm/slub: remove useless kmem_cache_debug

[Abel Wu]

On 2020/8/11 3:44, David Rientjes wrote:
> On Mon, 10 Aug 2020, wuyun.wu@xxxxxxxxxx wrote:
> 
>> From: Abel Wu <wuyun.wu@xxxxxxxxxx>
>>
>> The commit below is incomplete, as it didn't handle the add_full() part.
>> commit a4d3f8916c65 ("slub: remove useless kmem_cache_debug() before remove_full()")
>>
>> Signed-off-by: Abel Wu <wuyun.wu@xxxxxxxxxx>
>> ---
>>  mm/slub.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index fe81773..0b021b7 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -2182,7 +2182,8 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page,
>>  		}
>>  	} else {
>>  		m = M_FULL;
>> -		if (kmem_cache_debug(s) && !lock) {
>> +#ifdef CONFIG_SLUB_DEBUG
>> +		if (!lock) {
>>  			lock = 1;
>>  			/*
>>  			 * This also ensures that the scanning of full
>> @@ -2191,6 +2192,7 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page,
>>  			 */
>>  			spin_lock(&n->list_lock);
>>  		}
>> +#endif
>>  	}
>>
>>  	if (l != m) {
> 
> This should be functionally safe, I'm wonder if it would make sense to 
> only check for SLAB_STORE_USER here instead of kmem_cache_debug(), 
> however, since that should be the only context in which we need the 
> list_lock for add_full()?  It seems more explicit.
> .
> 
Yes, checking for SLAB_STORE_USER here can also get rid of noising macros.
I will resend the patch later.

Thanks,
	Abel