linux-kernel - Re: [PULL] Wrapper macros for struct task_struct and struct mm

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Message-Id: <200903121745.23448.rusty@rustcorp.com.au>
Date:	Thu, 12 Mar 2009 17:45:22 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PULL] Wrapper macros for struct task_struct and struct mm_struct cpumask transition

On Thursday 12 March 2009 14:50:11 Nick Piggin wrote:
> On Thursday 12 March 2009 15:06:52 Rusty Russell wrote:
> > Rusty Russell (2):
> >       cpumask: tsk_cpumask for accessing the struct task_struct's cpus_allowed.
> >       cpumask: mm_cpumask for accessing the struct mm_struct's cpu_vm_mask.
> >
> >  include/linux/mm_types.h |    3 +++
> >  include/linux/sched.h    |    3 +++
> 
> What's the transition?

Generally, cpumask_t to cpumask_var_t, ie. a struct cpumask [1] normally,
or a struct cpumask * for CONFIG_CPUMASK_OFFSTACK=y (currently x86 only).

In these cases though, we're allocating them anyway so it makes more sense to
do a dangling bitmap at the end of the struct (and only allocate nr_cpu_ids
bits when CONFIG_CPUMASK_OFFSTACK=y).

I had a patch which used a const struct cpumask * for task_struct: we only
ever replace the whole thing, so we can often use the standard cpu_mask_all
or cpumask_of() and only allocate when it's set to something else.  But
the code was pretty ugly.

Anyway, it's a trivial to change if people use the wrappers.  And if the
wrappers are in Linus' tree, it's easy to get the conversions into linux-next.

Cheers,
Rusty.
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