Messages in this thread | | | Date | Wed, 15 Apr 2009 13:41:54 +0200 | From | Andrea Arcangeli <> | Subject | Re: [RFC][PATCH v3 1/6] mm: Don't unmap gup()ed page |
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On Wed, Apr 15, 2009 at 08:39:04PM +0900, KOSAKI Motohiro wrote: > >> + if (!migration) { > >> + /* re-check */ > >> + if (PageSwapCache(page) && > >> + page_count(page) != page_mapcount(page) + 2) { > >> + /* We lose race against get_user_pages_fast() */ > >> + set_pte_at(mm, address, pte, pteval); > >> + ret = SWAP_FAIL; > >> + goto out_unmap; > >> + } > >> + } > >> + mmu_notifier_invalidate_page(vma->vm_mm, address); > > > > With regard to mmu notifier, this is the opposite of the right > > ordering. One mmu_notifier_invalidate_page must run _before_ the first > > check. The ptep_clear_flush_notify will then stay and there's no need > > of a further mmu_notifier_invalidate_page after the second check. > > OK. but I have one question. > > Can we assume mmu_notifier is only used by kvm now? > if not, we need to make new notifier.
KVM is no fundamentally different from other users in this respect, so I don't see why need a new notifier. If it works for others it'll work for KVM and the other way around is true too.
mmu notifier users can or cannot take a page pin. KVM does. GRU doesn't. XPMEM does. All of them releases any pin after mmu_notifier_invalidate_page. All that is important is to run mmu_notifier_invalidate_page _after_ the ptep_clear_young_notify, so that we don't nuke secondary mappings on the pages unless we really go to nuke the pte. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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