Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755612Ab3GYKq1 (ORCPT ); Thu, 25 Jul 2013 06:46:27 -0400 Received: from e06smtp11.uk.ibm.com ([195.75.94.107]:35699 "EHLO e06smtp11.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751750Ab3GYKqY (ORCPT ); Thu, 25 Jul 2013 06:46:24 -0400 Message-ID: <51F101F9.3090308@de.ibm.com> Date: Thu, 25 Jul 2013 12:46:17 +0200 From: Christian Borntraeger User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130623 Thunderbird/17.0.7 MIME-Version: 1.0 To: Martin Schwidefsky CC: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Andrew Morton , Mel Gorman , Nick Piggin , Hugh Dickins , Rik van Riel , Konstantin Weitz Subject: Re: [PATCH 1/2] mm: add support for discard of unused ptes References: <1374742461-29160-1-git-send-email-schwidefsky@de.ibm.com> <1374742461-29160-2-git-send-email-schwidefsky@de.ibm.com> In-Reply-To: <1374742461-29160-2-git-send-email-schwidefsky@de.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13072510-5024-0000-0000-000006AFBB06 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2771 Lines: 75 On 25/07/13 10:54, Martin Schwidefsky wrote: > From: Konstantin Weitz > > In a virtualized environment and given an appropriate interface the guest > can mark pages as unused while they are free (for the s390 implementation > see git commit 45e576b1c3d00206 "guest page hinting light"). For the host > the unused state is a property of the pte. > > This patch adds the primitive 'pte_unused' and code to the host swap out > handler so that pages marked as unused by all mappers are not swapped out > but discarded instead, thus saving one IO for swap out and potentially > another one for swap in. > > [ Martin Schwidefsky: patch reordering and simplification ] > > Signed-off-by: Konstantin Weitz > Signed-off-by: Martin Schwidefsky Reviewed-by: Christian Borntraeger > --- > include/asm-generic/pgtable.h | 13 +++++++++++++ > mm/rmap.c | 10 ++++++++++ > 2 files changed, 23 insertions(+) > > diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h > index 2f47ade..ec540c5 100644 > --- a/include/asm-generic/pgtable.h > +++ b/include/asm-generic/pgtable.h > @@ -193,6 +193,19 @@ static inline int pte_same(pte_t pte_a, pte_t pte_b) > } > #endif > > +#ifndef __HAVE_ARCH_PTE_UNUSED > +/* > + * Some architectures provide facilities to virtualization guests > + * so that they can flag allocated pages as unused. This allows the > + * host to transparently reclaim unused pages. This function returns > + * whether the pte's page is unused. > + */ > +static inline int pte_unused(pte_t pte) > +{ > + return 0; > +} > +#endif > + > #ifndef __HAVE_ARCH_PMD_SAME > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b) > diff --git a/mm/rmap.c b/mm/rmap.c > index cd356df..2291f25 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1234,6 +1234,16 @@ int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > } > set_pte_at(mm, address, pte, > swp_entry_to_pte(make_hwpoison_entry(page))); > + } else if (pte_unused(pteval)) { > + /* > + * The guest indicated that the page content is of no > + * interest anymore. Simply discard the pte, vmscan > + * will take care of the rest. > + */ > + if (PageAnon(page)) > + dec_mm_counter(mm, MM_ANONPAGES); > + else > + dec_mm_counter(mm, MM_FILEPAGES); > } else if (PageAnon(page)) { > swp_entry_t entry = { .val = page_private(page) }; > -- 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/