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

[Izik Eidus]

Andrew Morton wrote:
> On Mon, 20 Apr 2009 04:36:06 +0300
> Izik Eidus <ieidus@xxxxxxxxxx> 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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