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Date: Sat, 24 Mar 2012 19:00:02 +0400
From: Konstantin Khlebnikov <khlebnikov@openvz.org>
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        "linux@arm.linux.org.uk" <linux@arm.linux.org.uk>
Subject: Re: [PATCH 00/16] mm: prepare for converting vm->vm_flags to 64-bit
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Konstantin Khlebnikov wrote:
> Benjamin Herrenschmidt wrote:
>> On Thu, 2012-03-22 at 14:39 +0900, Minchan Kim wrote:
>>> I think we can also unify VM_MAPPED_COPY(nommu) and VM_SAO(powerpc)
>>> with one VM_ARCH_1
>>> Okay. After this series is merged, let's try to remove flags we can
>>> do. Then, other guys
>>> might suggest another ideas.
>>
>> Agreed. I would like more VM_ARCH while at it :-)
>
> Currently I see here four architecture-specific flags =)
>
> VM_ARCH_1 VM_ARCH_2 VM_ARCH_3 VM_ARCH_4
> x86 VM_NOHUGEPAGE VM_HUGEPAGE - VM_PFN_AT_MMAP
> powerpc - - VM_SAO -
> parisc VM_GROWSUP - - -
> ia64 VM_GROWSUP - - -
> nommu - VM_MAPPED_COPY - -
>
> Obviously we can combine VM_PFN_AT_MMAP, VM_SAO, VM_GROWSUP and VM_MAPPED_COPY into one.

Also logic and usage of VM_IO, VM_RESERVED, VM_PFNMAP, VM_MIXEDMAP,
VM_INSERTPAGE, VM_DONTEXPAND and VM_DONTCOPY are very messy.
I think some of them can be replaced with two flags:
VM_SPECIAL_PFN and VM_SPECIAL_PAGE, or something like this.