linux-kernel - Re: [PATCH v2 3/3] cpuset: PF_SPREAD_PAGE and PF_SPREAD

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Date:	Wed, 24 Sep 2014 11:01:04 +0800
From:	Zefan Li <lizefan@...wei.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
CC:	<tj@...nel.org>, <peterz@...radead.org>, <mingo@...nel.org>,
	<miaox@...fujitsu.com>, <linux-kernel@...r.kernel.org>,
	<cgroups@...r.kernel.org>, <keescook@...omium.org>
Subject: Re: [PATCH v2 3/3] cpuset: PF_SPREAD_PAGE and PF_SPREAD_SLAB should
 beatomic flags

On 2014/9/23 18:55, Tetsuo Handa wrote:
> Zefan Li wrote:
>> Tetsuo reported a hard-to-reproduce kernel crash on RHEL6, which happend
> 
> s/happend/happened/
> 
>> @@ -1972,6 +1973,14 @@ static inline void memalloc_noio_restore(unsigned int flags)
>>  TASK_PFA_TEST(NO_NEW_PRIVS, no_new_privs)
>>  TASK_PFA_SET(NO_NEW_PRIVS, no_new_privs)
>>  
>> +TASK_PFA_TEST(SPREAD_PAGE, spread_page)
>> +TASK_PFA_SET(SPREAD_PAGE, spread_page)
>> +TASK_PFA_CLEAR(SPREAD_PAGE, spread_page)
>> +
>> +TASK_PFA_TEST(SPREAD_SLAB, spread_slab)
>> +TASK_PFA_SET(SPREAD_SLAB, spread_slab)
>> +TASK_PFA_CLEAR(SPREAD_SLAB, spread_slab)
>> +
> 
> I wonder how adding 3 macro lines differs from 3 inlined functions.
> Personally, from LXR (source code browser) point of view, inlined functions
> are more friendly than macros. Also, I wonder about the cost of extracting
> macros in a file which is likely included by every file but referenced
> by few files. Speak of SPREAD_PAGE and SPREAD_SLAB, they should be defined
> as inlined functions in include/linux/cpuset.h rather than as macros in
> include/linux/sched.h ?
> .

Though tsk->atomic_flags were newly introduced in 3.17 merge window, we
already have 3 flags, and we may see more flags added.

Those macros make the code easier to read, and emacs and cscope can also
understand them.

I'd vote for this:

TASK_PFA_TEST(NO_NEW_PRIVS, no_new_privs)
TASK_PFA_SET(NO_NEW_PRIVS, no_new_privs)

TASK_PFA_TEST(SPREAD_PAGE, spread_page)
TASK_PFA_SET(SPREAD_PAGE, spread_page)
TASK_PFA_CLEAR(SPREAD_PAGE, spread_page)

TASK_PFA_TEST(SPREAD_SLAB, spread_slab)
TASK_PFA_SET(SPREAD_SLAB, spread_slab)
TASK_PFA_CLEAR(SPREAD_SLAB, spread_slab)

over this:

static inline bool task_no_new_privs(struct task_struct *p)
{
	return test_bit(PFA_NO_NEW_PRIVS, &p->atomic_flags);
}
static inline void task_set_new_privs(struct task_struct *p)
{
	set_bit(PFA_NO_NEW_PRIVS, &p->atomic_flags);
}

static inline bool task_spread_page(struct task_struct *p)
{
	return test_bit(PFA_SPREAD_PAGE, &p->atomic_flags);
}
static inline void task_set_spread_page(struct task_struct *p)
{
	set_bit(PFA_SPREAD_PAGE, &p->atomic_flags);
}
static inline void task_clear_spread_page(struct task_struct *p)
{
	clear_bit(PFA_SPREAD_PAGE, &p->atomic_flags);
}

static inline bool task_spread_slab(struct task_struct *p)
{
	return test_bit(PFA_SPREAD_SLAB, &p->atomic_flags);
}
static inline void task_set_spread_slab(struct task_struct *p)
{
	set_bit(PFA_SPREAD_SLAB, &p->atomic_flags);
}
static inline void task_clear_spread_slab(struct task_struct *p)
{
	clear_bit(PFA_SPREAD_SLAB, &p->atomic_flags);
}


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