linux-kernel - Re: [PATCH 5/5] add ksm kernel shared memory driver.

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Message-Id: <20090427153421.2682291f.akpm@linux-foundation.org>
Date:	Mon, 27 Apr 2009 15:34:21 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Izik Eidus <ieidus@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kvm@...r.kernel.org, avi@...hat.com, aarcange@...hat.com,
	chrisw@...hat.com, mtosatti@...hat.com, hugh@...itas.com,
	ieidus@...hat.com
Subject: Re: [PATCH 5/5] add ksm kernel shared memory driver.

On Mon, 20 Apr 2009 04:36:06 +0300
Izik Eidus <ieidus@...hat.com> wrote:

> Ksm is driver that allow merging identical pages between one or more
> applications in way unvisible to the application that use it.
> Pages that are merged are marked as readonly and are COWed when any
> application try to change them.

Breaks sparc64 and probably lots of other architectures:

mm/ksm.c: In function `try_to_merge_two_pages_alloc':
mm/ksm.c:697: error: `_PAGE_RW' undeclared (first use in this function)

there should be an official arch-independent way of manipulating
vma->vm_page_prot, but I'm not immediately finding it.

An alternative (and quite inferior) "fix" would be to disable ksm on
architectures which don't implement _PAGE_RW.  That's most of them.

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