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[209.132.183.28]) by mx.google.com with ESMTPS id t126si2919271qkc.5.2019.02.11.09.41.18 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Feb 2019 09:41:19 -0800 (PST) Received-SPF: pass (google.com: domain of mst@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of mst@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=mst@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 08DE5C01DE19; Mon, 11 Feb 2019 17:41:18 +0000 (UTC) Received: from redhat.com (ovpn-120-40.rdu2.redhat.com [10.10.120.40]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7A7962D321; Mon, 11 Feb 2019 17:41:08 +0000 (UTC) Date: Mon, 11 Feb 2019 12:41:08 -0500 From: "Michael S. Tsirkin" To: Nitesh Narayan Lal Cc: Alexander Duyck , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, rkrcmar@redhat.com, alexander.h.duyck@linux.intel.com, x86@kernel.org, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, pbonzini@redhat.com, tglx@linutronix.de, akpm@linux-foundation.org Subject: Re: [RFC PATCH 4/4] mm: Add merge page notifier Message-ID: <20190211123815-mutt-send-email-mst@kernel.org> References: <20190204181118.12095.38300.stgit@localhost.localdomain> <20190204181558.12095.83484.stgit@localhost.localdomain> <20190209195325-mutt-send-email-mst@kernel.org> <7fcb61d6-64f0-f3ae-5e32-0e9f587fdd49@redhat.com> <20190211091623-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Mon, 11 Feb 2019 17:41:18 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Feb 11, 2019 at 11:24:02AM -0500, Nitesh Narayan Lal wrote: > > On 2/11/19 9:17 AM, Michael S. Tsirkin wrote: > > On Mon, Feb 11, 2019 at 08:30:03AM -0500, Nitesh Narayan Lal wrote: > >> On 2/9/19 7:57 PM, Michael S. Tsirkin wrote: > >>> On Mon, Feb 04, 2019 at 10:15:58AM -0800, Alexander Duyck wrote: > >>>> From: Alexander Duyck > >>>> > >>>> Because the implementation was limiting itself to only providing hints on > >>>> pages huge TLB order sized or larger we introduced the possibility for free > >>>> pages to slip past us because they are freed as something less then > >>>> huge TLB in size and aggregated with buddies later. > >>>> > >>>> To address that I am adding a new call arch_merge_page which is called > >>>> after __free_one_page has merged a pair of pages to create a higher order > >>>> page. By doing this I am able to fill the gap and provide full coverage for > >>>> all of the pages huge TLB order or larger. > >>>> > >>>> Signed-off-by: Alexander Duyck > >>> Looks like this will be helpful whenever active free page > >>> hints are added. So I think it's a good idea to > >>> add a hook. > >>> > >>> However, could you split adding the hook to a separate > >>> patch from the KVM hypercall based implementation? > >>> > >>> Then e.g. Nilal's patches could reuse it too. > >> With the current design of my patch-set, if I use this hook to report > >> free pages. I will end up making redundant hints for the same pfns. > >> > >> This is because the pages once freed by the host, are returned back to > >> the buddy. > > Suggestions on how you'd like to fix this? You do need this if > > you introduce a size cut-off right? > > I do, there are two ways to go about it. > > One is to  use this and have a flag in the page structure indicating > whether that page has been freed/used or not. Not sure what do you mean. The refcount does this right? > Though I am not sure if > this will be acceptable upstream. > Second is to find another place to invoke guest_free_page() post buddy > merging. Might be easier. > > > >>> > >>>> --- > >>>> arch/x86/include/asm/page.h | 12 ++++++++++++ > >>>> arch/x86/kernel/kvm.c | 28 ++++++++++++++++++++++++++++ > >>>> include/linux/gfp.h | 4 ++++ > >>>> mm/page_alloc.c | 2 ++ > >>>> 4 files changed, 46 insertions(+) > >>>> > >>>> diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h > >>>> index 4487ad7a3385..9540a97c9997 100644 > >>>> --- a/arch/x86/include/asm/page.h > >>>> +++ b/arch/x86/include/asm/page.h > >>>> @@ -29,6 +29,18 @@ static inline void arch_free_page(struct page *page, unsigned int order) > >>>> if (static_branch_unlikely(&pv_free_page_hint_enabled)) > >>>> __arch_free_page(page, order); > >>>> } > >>>> + > >>>> +struct zone; > >>>> + > >>>> +#define HAVE_ARCH_MERGE_PAGE > >>>> +void __arch_merge_page(struct zone *zone, struct page *page, > >>>> + unsigned int order); > >>>> +static inline void arch_merge_page(struct zone *zone, struct page *page, > >>>> + unsigned int order) > >>>> +{ > >>>> + if (static_branch_unlikely(&pv_free_page_hint_enabled)) > >>>> + __arch_merge_page(zone, page, order); > >>>> +} > >>>> #endif > >>>> > >>>> #include > >>>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > >>>> index 09c91641c36c..957bb4f427bb 100644 > >>>> --- a/arch/x86/kernel/kvm.c > >>>> +++ b/arch/x86/kernel/kvm.c > >>>> @@ -785,6 +785,34 @@ void __arch_free_page(struct page *page, unsigned int order) > >>>> PAGE_SIZE << order); > >>>> } > >>>> > >>>> +void __arch_merge_page(struct zone *zone, struct page *page, > >>>> + unsigned int order) > >>>> +{ > >>>> + /* > >>>> + * The merging logic has merged a set of buddies up to the > >>>> + * KVM_PV_UNUSED_PAGE_HINT_MIN_ORDER. Since that is the case, take > >>>> + * advantage of this moment to notify the hypervisor of the free > >>>> + * memory. > >>>> + */ > >>>> + if (order != KVM_PV_UNUSED_PAGE_HINT_MIN_ORDER) > >>>> + return; > >>>> + > >>>> + /* > >>>> + * Drop zone lock while processing the hypercall. This > >>>> + * should be safe as the page has not yet been added > >>>> + * to the buddy list as of yet and all the pages that > >>>> + * were merged have had their buddy/guard flags cleared > >>>> + * and their order reset to 0. > >>>> + */ > >>>> + spin_unlock(&zone->lock); > >>>> + > >>>> + kvm_hypercall2(KVM_HC_UNUSED_PAGE_HINT, page_to_phys(page), > >>>> + PAGE_SIZE << order); > >>>> + > >>>> + /* reacquire lock and resume freeing memory */ > >>>> + spin_lock(&zone->lock); > >>>> +} > >>>> + > >>>> #ifdef CONFIG_PARAVIRT_SPINLOCKS > >>>> > >>>> /* Kick a cpu by its apicid. Used to wake up a halted vcpu */ > >>>> diff --git a/include/linux/gfp.h b/include/linux/gfp.h > >>>> index fdab7de7490d..4746d5560193 100644 > >>>> --- a/include/linux/gfp.h > >>>> +++ b/include/linux/gfp.h > >>>> @@ -459,6 +459,10 @@ static inline struct zonelist *node_zonelist(int nid, gfp_t flags) > >>>> #ifndef HAVE_ARCH_FREE_PAGE > >>>> static inline void arch_free_page(struct page *page, int order) { } > >>>> #endif > >>>> +#ifndef HAVE_ARCH_MERGE_PAGE > >>>> +static inline void > >>>> +arch_merge_page(struct zone *zone, struct page *page, int order) { } > >>>> +#endif > >>>> #ifndef HAVE_ARCH_ALLOC_PAGE > >>>> static inline void arch_alloc_page(struct page *page, int order) { } > >>>> #endif > >>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c > >>>> index c954f8c1fbc4..7a1309b0b7c5 100644 > >>>> --- a/mm/page_alloc.c > >>>> +++ b/mm/page_alloc.c > >>>> @@ -913,6 +913,8 @@ static inline void __free_one_page(struct page *page, > >>>> page = page + (combined_pfn - pfn); > >>>> pfn = combined_pfn; > >>>> order++; > >>>> + > >>>> + arch_merge_page(zone, page, order); > >>>> } > >>>> if (max_order < MAX_ORDER) { > >>>> /* If we are here, it means order is >= pageblock_order. > >> -- > >> Regards > >> Nitesh > >> > > > > > -- > Regards > Nitesh >