Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757770Ab3G3UoZ (ORCPT ); Tue, 30 Jul 2013 16:44:25 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:47357 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756924Ab3G3UoX (ORCPT ); Tue, 30 Jul 2013 16:44:23 -0400 Date: Tue, 30 Jul 2013 13:44:22 -0700 From: Andrew Morton To: Martin Schwidefsky Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Mel Gorman , Nick Piggin , Hugh Dickins , Rik van Riel , Konstantin Weitz Subject: Re: [PATCH 1/2] mm: add support for discard of unused ptes Message-Id: <20130730134422.98c0977eada81d3ac41a08bb@linux-foundation.org> In-Reply-To: <1374742461-29160-2-git-send-email-schwidefsky@de.ibm.com> References: <1374742461-29160-1-git-send-email-schwidefsky@de.ibm.com> <1374742461-29160-2-git-send-email-schwidefsky@de.ibm.com> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2440 Lines: 66 On Thu, 25 Jul 2013 10:54:20 +0200 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. > > ... > > --- 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) }; Obviously harmless. Please include this in whatever tree carries "[PATCH 2/2] s390/kvm: support collaborative memory management". -- 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/