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Subject: Re: [PATCH] mm/slub: remove useless kmem_cache_debug
To:     David Rientjes <rientjes@google.com>
CC:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        <liu.xiang6@zte.com.cn>,
        "open list:SLAB ALLOCATOR" <linux-mm@kvack.org>,
        open list <linux-kernel@vger.kernel.org>
References: <20200810080758.940-1-wuyun.wu@huawei.com>
 <alpine.DEB.2.23.453.2008101244090.2938695@chino.kir.corp.google.com>
From:   Abel Wu <wuyun.wu@huawei.com>
Message-ID: <63ee904c-f6b7-3a00-c51d-3ff0feabc9d6@huawei.com>
Date:   Tue, 11 Aug 2020 09:29:38 +0800
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On 2020/8/11 3:44, David Rientjes wrote:
> On Mon, 10 Aug 2020, wuyun.wu@huawei.com wrote:
> 
>> From: Abel Wu <wuyun.wu@huawei.com>
>>
>> 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@huawei.com>
>> ---
>>  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