linux-kernel - Re: [PATCH 2/5] mm/slub: query dynamic DEBUG

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Message-ID: <CAAmzW4Oce1zeVj=cjcgNVYV8CSE6JbQgdDbxroTrBMt02C13Yw@mail.gmail.com>
Date:	Fri, 5 Feb 2016 01:21:12 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Takashi Iwai <tiwai@...e.com>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Christoph Lameter <cl@...ux.com>, linux-api@...r.kernel.org,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 2/5] mm/slub: query dynamic DEBUG_PAGEALLOC setting

2016-02-04 17:31 GMT+09:00 Christian Borntraeger <borntraeger@...ibm.com>:
> On 02/04/2016 06:56 AM, Joonsoo Kim wrote:
>> We can disable debug_pagealloc processing even if the code is complied
>> with CONFIG_DEBUG_PAGEALLOC. This patch changes the code to query
>> whether it is enabled or not in runtime.
>>
>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>> ---
>>  mm/slub.c | 11 ++++++-----
>>  1 file changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 7d4da68..7b5a965 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -256,11 +256,12 @@ static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
>>  {
>>       void *p;
>>
>> -#ifdef CONFIG_DEBUG_PAGEALLOC
>> -     probe_kernel_read(&p, (void **)(object + s->offset), sizeof(p));
>> -#else
>> -     p = get_freepointer(s, object);
>> -#endif
>> +     if (debug_pagealloc_enabled()) {
>> +             probe_kernel_read(&p,
>> +                     (void **)(object + s->offset), sizeof(p));
>
> Hmm, this might be a good case for a line longer than 80 chars....
>
> As an alternative revert the logic and return early:
>
>
>         if (!debug_pagealloc_enabled())
>                 return get_freepointer(s, object);
>         probe_kernel_read(&p, (void **)(object + s->offset), sizeof(p));
>         return p;
>

Looks better!
I will fix it on next version.

Thanks.