Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755272Ab3GYIzk (ORCPT ); Thu, 25 Jul 2013 04:55:40 -0400 Received: from e06smtp10.uk.ibm.com ([195.75.94.106]:40754 "EHLO e06smtp10.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754862Ab3GYIzR (ORCPT ); Thu, 25 Jul 2013 04:55:17 -0400 From: Martin Schwidefsky To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Andrew Morton , Mel Gorman , Nick Piggin , Hugh Dickins , Rik van Riel Cc: Martin Schwidefsky , Konstantin Weitz Subject: [PATCH 1/2] mm: add support for discard of unused ptes Date: Thu, 25 Jul 2013 10:54:20 +0200 Message-Id: <1374742461-29160-2-git-send-email-schwidefsky@de.ibm.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1374742461-29160-1-git-send-email-schwidefsky@de.ibm.com> References: <1374742461-29160-1-git-send-email-schwidefsky@de.ibm.com> X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13072508-4966-0000-0000-0000066154FE Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2547 Lines: 74 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 --- 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) }; -- 1.7.9.5 -- 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/