linux-kernel - Re: mm: convert vma->vm

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Date:	Sun, 17 Apr 2011 17:26:19 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: mm: convert vma->vm_flags to 64bit

On Tue, 12 Apr 2011, KOSAKI Motohiro wrote:
> 
> Benjamin, Hugh, I hope to add your S-O-B to this one because you are original author. 
> Can I do?

Well, now you've fixed the mm/fremap.c omission, you're welcome to my
Acked-by: Hugh Dickins <hughd@...gle.com>

I happen not to shared Ben's aversion to unsigned long long, I just
don't really care one way or another on that; but I do get irritated by
obfuscatory types which we then have to cast or unfold all over the place,
I don't know if vm_flags_t would have been in that category or not.

You've made a few different choices than I did, okay: the only place
where it might be worth disagreeing with you, is on mm->def_flags:
I would rather make that an unsigned int than an unsigned long long,
to save 4 bytes on 64-bit (if it were moved) rather than waste 4 bytes
on 32-bit - in the unlikely event that someone adds a high VM_flag to
def_flags, I'd rather hope they would test its effect.  However,
it's every mm not every vma, so maybe not worth worrying about.

I am surprised that
#define VM_EXEC		0x00000004ULL
does not cause trouble for arch/arm/kernel/asm-offsets.c,
but you tried cross-building it which I never did.

Does your later addition of __nocast on vm_flags not make trouble
for the unsigned long casts in arch/arm/include/asm/cacheflush.h?
(And if it does not, then just what does __nocast do?)

Thanks for seeing this through,
Hugh
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