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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. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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