linux-kernel - Re: [RFC][PATCH] x86, fpu: dynamically allocate 'struct fpu'

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Date:	Thu, 16 Jul 2015 14:29:02 -0700
From:	Dave Hansen <dave@...1.net>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] x86, fpu: dynamically allocate 'struct fpu'

On 07/16/2015 12:25 PM, Andy Lutomirski wrote:
> On Thu, Jul 16, 2015 at 12:14 PM, Dave Hansen <dave@...1.net> wrote:
>> +#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER)   \
>> +       BUILD_BUG_ON((sizeof(TYPE) -                    \
>> +                       offsetof(TYPE, MEMBER) -        \
>> +                       sizeof(((TYPE *)0)->MEMBER)) >  \
>> +                       0)                              \
>> +
> 
> You could save a bit of typing by using offsetofend here.  Something
> along the lines of BUILD_BUG_ON(sizeof(TYPE) != offsetofend(TYPE,
> MEMBER));

Good point.

>>  #endif /* _ASM_X86_FPU_H */
>> diff -puN arch/x86/kernel/process.c~dynamically-allocate-struct-fpu arch/x86/kernel/process.c
>> --- a/arch/x86/kernel/process.c~dynamically-allocate-struct-fpu 2015-07-16 10:50:42.360571875 -0700
>> +++ b/arch/x86/kernel/process.c 2015-07-16 12:00:59.204808551 -0700
>> @@ -81,7 +81,7 @@ EXPORT_SYMBOL_GPL(idle_notifier_unregist
>>   */
>>  int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
>>  {
>> -       *dst = *src;
>> +       memcpy(dst, src, arch_task_struct_size());
> 
> This is actually vaguely performance-critical, which makes me thing
> that using some kind of inline or other real way (config macro, ifdef,
> etc) to detect whether there's an arch override would be better than a
> weak function.

Fair enough.  I'll send out another version in a bit if there are no
more comments.
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