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

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Message-ID: <4A0B6289.2000502@redhat.com>
Date:	Thu, 14 May 2009 03:15:05 +0300
From:	Izik Eidus <ieidus@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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
Subject: Re: [PATCH 5/5] add ksm kernel shared memory driver.

Andrew Morton wrote:
> 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.
>>
>> Ksm is used for cases where using fork() is not suitable,
>> one of this cases is where the pages of the application keep changing
>> dynamicly and the application cannot know in advance what pages are
>> going to be identical.
>>
>> Ksm works by walking over the memory pages of the applications it
>> scan in order to find identical pages.
>> It uses a two sorted data strctures called stable and unstable trees
>> to find in effective way the identical pages.
>>
>> When ksm finds two identical pages, it marks them as readonly and merges
>> them into single one page,
>> after the pages are marked as readonly and merged into one page, linux
>> will treat this pages as normal copy_on_write pages and will fork them
>> when write access will happen to them.
>>
>> Ksm scan just memory areas that were registred to be scanned by it.
>>
>> ...
>> +	copy_user_highpage(kpage, page1, addr1, vma);
>> ...
>>     
>
> Breaks ppc64 allmodcofnig because that architecture doesn't export its
> copy_user_page() to modules.
>
> Architectures are inconsistent about this.  x86 _does_ export it,
> because it bounces it to the exported copy_page().
>
> So can I ask that you sit down and work out upon which architectures it
> really makes sense to offer KSM?  Disallow the others in Kconfig and
> arrange for copy_user_highpage() to be available on the allowed architectures?
>   

Hi

There is some way (script) that i can run that will allow compile this 
code for every possible arch?

(I dont mind to allow it just for archs that support virtualization - 
x86, ia64, powerpc, s390, but is it the right thing to do ?)
> Thanks.
>   

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