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[209.132.180.67]) by mx.google.com with ESMTP id t22si2881023pgv.190.2019.02.08.13.31.43; Fri, 08 Feb 2019 13:32:04 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727266AbfBHVbh (ORCPT + 99 others); Fri, 8 Feb 2019 16:31:37 -0500 Received: from mga09.intel.com ([134.134.136.24]:4946 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727182AbfBHVbh (ORCPT ); Fri, 8 Feb 2019 16:31:37 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 08 Feb 2019 13:31:36 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,348,1544515200"; d="scan'208";a="137020789" Received: from ahduyck-desk1.jf.intel.com ([10.7.198.76]) by orsmga001.jf.intel.com with ESMTP; 08 Feb 2019 13:31:36 -0800 Message-ID: Subject: Re: [RFC PATCH 3/4] kvm: Add guest side support for free memory hints From: Alexander Duyck To: Nitesh Narayan Lal , Luiz Capitulino , Alexander Duyck Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, rkrcmar@redhat.com, x86@kernel.org, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, pbonzini@redhat.com, tglx@linutronix.de, akpm@linux-foundation.org Date: Fri, 08 Feb 2019 13:31:36 -0800 In-Reply-To: <5f5c03ac-0d21-d92b-1772-f26773437019@redhat.com> References: <20190204181118.12095.38300.stgit@localhost.localdomain> <20190204181552.12095.46287.stgit@localhost.localdomain> <20190207132104.17a296da@doriath> <34c93e5a05a7dc93e38364733f8832f2e1b2dcb3.camel@linux.intel.com> <5f5c03ac-0d21-d92b-1772-f26773437019@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-2.fc28) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2019-02-08 at 16:05 -0500, Nitesh Narayan Lal wrote: > On 2/7/19 1:44 PM, Alexander Duyck wrote: > > On Thu, 2019-02-07 at 13:21 -0500, Luiz Capitulino wrote: > > > On Mon, 04 Feb 2019 10:15:52 -0800 > > > Alexander Duyck wrote: > > > > > > > From: Alexander Duyck > > > > > > > > Add guest support for providing free memory hints to the KVM hypervisor for > > > > freed pages huge TLB size or larger. I am restricting the size to > > > > huge TLB order and larger because the hypercalls are too expensive to be > > > > performing one per 4K page. Using the huge TLB order became the obvious > > > > choice for the order to use as it allows us to avoid fragmentation of higher > > > > order memory on the host. > > > > > > > > I have limited the functionality so that it doesn't work when page > > > > poisoning is enabled. I did this because a write to the page after doing an > > > > MADV_DONTNEED would effectively negate the hint, so it would be wasting > > > > cycles to do so. > > > > > > > > Signed-off-by: Alexander Duyck > > > > --- > > > > arch/x86/include/asm/page.h | 13 +++++++++++++ > > > > arch/x86/kernel/kvm.c | 23 +++++++++++++++++++++++ > > > > 2 files changed, 36 insertions(+) > > > > > > > > diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h > > > > index 7555b48803a8..4487ad7a3385 100644 > > > > --- a/arch/x86/include/asm/page.h > > > > +++ b/arch/x86/include/asm/page.h > > > > @@ -18,6 +18,19 @@ > > > > > > > > struct page; > > > > > > > > +#ifdef CONFIG_KVM_GUEST > > > > +#include > > > > +extern struct static_key_false pv_free_page_hint_enabled; > > > > + > > > > +#define HAVE_ARCH_FREE_PAGE > > > > +void __arch_free_page(struct page *page, unsigned int order); > > > > +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); > > > > +} > > > > +#endif > > > > + > > > > #include > > > > extern struct range pfn_mapped[]; > > > > extern int nr_pfn_mapped; > > > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > > > > index 5c93a65ee1e5..09c91641c36c 100644 > > > > --- a/arch/x86/kernel/kvm.c > > > > +++ b/arch/x86/kernel/kvm.c > > > > @@ -48,6 +48,7 @@ > > > > #include > > > > > > > > static int kvmapf = 1; > > > > +DEFINE_STATIC_KEY_FALSE(pv_free_page_hint_enabled); > > > > > > > > static int __init parse_no_kvmapf(char *arg) > > > > { > > > > @@ -648,6 +649,15 @@ static void __init kvm_guest_init(void) > > > > if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) > > > > apic_set_eoi_write(kvm_guest_apic_eoi_write); > > > > > > > > + /* > > > > + * The free page hinting doesn't add much value if page poisoning > > > > + * is enabled. So we only enable the feature if page poisoning is > > > > + * no present. > > > > + */ > > > > + if (!page_poisoning_enabled() && > > > > + kvm_para_has_feature(KVM_FEATURE_PV_UNUSED_PAGE_HINT)) > > > > + static_branch_enable(&pv_free_page_hint_enabled); > > > > + > > > > #ifdef CONFIG_SMP > > > > smp_ops.smp_prepare_cpus = kvm_smp_prepare_cpus; > > > > smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu; > > > > @@ -762,6 +772,19 @@ static __init int kvm_setup_pv_tlb_flush(void) > > > > } > > > > arch_initcall(kvm_setup_pv_tlb_flush); > > > > > > > > +void __arch_free_page(struct page *page, unsigned int order) > > > > +{ > > > > + /* > > > > + * Limit hints to blocks no smaller than pageblock in > > > > + * size to limit the cost for the hypercalls. > > > > + */ > > > > + if (order < KVM_PV_UNUSED_PAGE_HINT_MIN_ORDER) > > > > + return; > > > > + > > > > + kvm_hypercall2(KVM_HC_UNUSED_PAGE_HINT, page_to_phys(page), > > > > + PAGE_SIZE << order); > > > > > > Does this mean that the vCPU executing this will get stuck > > > here for the duration of the hypercall? Isn't that too long, > > > considering that the zone lock is taken and madvise in the > > > host block on semaphores? > > > > I'm pretty sure the zone lock isn't held when this is called. The lock > > isn't acquired until later in the path. This gets executed just before > > the page poisoning call which would take time as well since it would > > have to memset an entire page. This function is called as a part of > > free_pages_prepare, the zone locks aren't acquired until we are calling > > into either free_one_page and a few spots before calling > > __free_one_page. > > > > My other function in patch 4 which does this from inside of > > __free_one_page does have to release the zone lock since it is taken > > there. > > > > Considering hypercall's are costly, will it not make sense to coalesce > the pages you are reporting and make a single hypercall for a bunch of > pages? That is what I am doing with this code and patch 4. I am only making the call when I have been given a page that is 2M or larger. As such I am only making one hypercall for every 512 4K pages. So for example on my test VMs with 8G of RAM I see only about 3K calls when it ends up freeing all of the application memory which is about 6G after my test has ended.