linux-kernel - Re: linux/kernel/sched.c: context

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Message-Id: <201009081554.08676.fabio@metanix.org>
Date:	Wed, 8 Sep 2010 15:54:07 +0200
From:	fabio de francesco <fabio@...anix.org>
To:	"chxanders@...il.com" <chxanders@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: linux/kernel/sched.c: context_switch().

On Wednesday 08 September 2010 15:22:07 you wrote:
> but there is a ! not operator, !mm means mm != 0 , or the other way it
> is saying it is unlikey(mm is NULL)

Ok. Let me point to Linux-2.6.32. You may see that there the opposite is 
written. Can you please explain why they changed unlikely with likely passing 
from 2.6.32 to 2.6.33?

> On 8 September 2010 20:18, fabio de francesco <fabio@...anix.org> wrote:
> > On Wednesday 08 September 2010 15:10:49 you wrote:
> >> Long day? Do you mean likely(!mm) actually means unlikely(0)?
> > 
> > No, no. I am sorry for my poor English. I mean:"likely(!mm) is like
> > "likely(0)".
> > 
> >> On 8 September 2010 20:08, fabio de francesco <fabio@...anix.org> wrote:
> >> > There must be something I am missing in sched.c at context_switch()
> >> > function definition.
> >> > 
> >> > There I can read the following code:
> >> > 
> >> > static inline void
> >> > context_switch(struct rq *rq, struct task_struct *prev,
> >> >               struct task_struct *next)
> >> > {
> >> >        ...
> >> >        struct mm_struct *mm;
> >> >        mm = next->mm;
> >> >        if (likely(!mm)) {
> >> >                next->active_mm = oldmm;
> >> >                atomic_inc(&oldmm->mm_count);
> >> >                enter_lazy_tlb(oldmm, next);
> >> >        } else
> >> >                switch_mm(oldmm, mm, next);
> >> >        ...
> >> > }
> >> > 
> >> > May someone please explain why the mm pointer is likely supposed to be
> >> > NULL?
> >> > 
> >> > Thanks in advance.
> >> > 
> >> > fabio
> >> > --
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