linux-kernel - Re: [PATCH 2/4] mm: introduce new VM

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Message-ID: <54419265.9000000@intel.com>
Date:	Fri, 17 Oct 2014 15:04:21 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Dominik Dingel <dingel@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	Rik van Riel <riel@...hat.com>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Bob Liu <lliubbo@...il.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Gleb Natapov <gleb@...nel.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Jianyu Zhan <nasa4836@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Konstantin Weitz <konstantin.weitz@...il.com>,
	kvm@...r.kernel.org, linux390@...ibm.com,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [PATCH 2/4] mm: introduce new VM_NOZEROPAGE flag

On 10/17/2014 07:09 AM, Dominik Dingel wrote:
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index cd33ae2..8f09c91 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -113,7 +113,7 @@ extern unsigned int kobjsize(const void *objp);
>  #define VM_GROWSDOWN	0x00000100	/* general info on the segment */
>  #define VM_PFNMAP	0x00000400	/* Page-ranges managed without "struct page", just pure PFN */
>  #define VM_DENYWRITE	0x00000800	/* ETXTBSY on write attempts.. */
> -
> +#define VM_NOZEROPAGE	0x00001000	/* forbid new zero page mappings */
>  #define VM_LOCKED	0x00002000
>  #define VM_IO           0x00004000	/* Memory mapped I/O or similar */

This seems like an awfully obscure use for a very constrained resource
(VM_ flags).

Is there ever a time where the VMAs under an mm have mixed VM_NOZEROPAGE
status?  Reading the patches, it _looks_ like it might be an all or
nothing thing.

Full disclosure: I've got an x86-specific feature I want to steal a flag
for.  Maybe we should just define another VM_ARCH bit.
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