From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx175.postini.com [74.125.245.175]) by kanga.kvack.org (Postfix) with SMTP id AD9996B0031 for ; Thu, 25 Jul 2013 06:46:22 -0400 (EDT) Received: from /spool/local by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 25 Jul 2013 11:41:38 +0100 Received: from b06cxnps3074.portsmouth.uk.ibm.com (d06relay09.portsmouth.uk.ibm.com [9.149.109.194]) by d06dlp02.portsmouth.uk.ibm.com (Postfix) with ESMTP id B4286219005A for ; Thu, 25 Jul 2013 11:50:28 +0100 (BST) Received: from d06av10.portsmouth.uk.ibm.com (d06av10.portsmouth.uk.ibm.com [9.149.37.251]) by b06cxnps3074.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r6PAk7cx786880 for ; Thu, 25 Jul 2013 10:46:07 GMT Received: from d06av10.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av10.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id r6PAkHlZ026551 for ; Thu, 25 Jul 2013 04:46:18 -0600 Message-ID: <51F101F9.3090308@de.ibm.com> Date: Thu, 25 Jul 2013 12:46:17 +0200 From: Christian Borntraeger MIME-Version: 1.0 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 Sender: owner-linux-mm@kvack.org List-ID: 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 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org