linux-kernel - Re: [PATCH] mm: don't access vm

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Date:	Thu, 26 May 2011 11:49:59 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	benh@...nel.crashing.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, hughd@...gle.com,
	akpm@...ux-foundation.org, dave@...ux.vnet.ibm.com,
	kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH] mm: don't access vm_flags as 'int'

On Thu, May 26, 2011 at 11:44 AM, Alexey Dobriyan <adobriyan@...il.com> wrote:
>
> Woo-hoo!
>
> Why it is marked __nocast and not __bitwise__ like gfp_t?

Because that's what one of the other patches in Andrew's series had,
so I just emulated that.

Also, I don't think we can currently mark it __bitwise without causing
a sh*tload of sparse warnings. __nocast is much weaker than bitwise
(it only warns about implicit casts to different sizes). __bitwise
implies a lot more type-checking, and actually makes the result a very
specific type.

I'm not sure it is worth the __bitwise pain. If we go down the
__bitwise path, we'd need to mark all the VM_XYZZY constants with the
type, and we'd need to do *all* the conversions in one go. I am
definitely not ready to do that at this stage, but I was willing to
take the much weaker __nocast.

                    Linus
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