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[192.55.52.120]) by mx.google.com with ESMTPS id h32si1358409pgh.276.2019.02.04.15.37.34 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 04 Feb 2019 15:37:34 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of alexander.h.duyck@linux.intel.com designates 192.55.52.120 as permitted sender) client-ip=192.55.52.120; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of alexander.h.duyck@linux.intel.com designates 192.55.52.120 as permitted sender) smtp.mailfrom=alexander.h.duyck@linux.intel.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 04 Feb 2019 15:37:34 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,560,1539673200"; d="scan'208";a="123953782" Received: from ahduyck-desk1.jf.intel.com ([10.7.198.76]) by orsmga003.jf.intel.com with ESMTP; 04 Feb 2019 15:37:33 -0800 Message-ID: Subject: Re: [RFC PATCH 3/4] kvm: Add guest side support for free memory hints From: Alexander Duyck To: Nadav Amit , Alexander Duyck Cc: Linux-MM , LKML , kvm list , Radim Krcmar , X86 ML , Ingo Molnar , bp@alien8.de, hpa@zytor.com, pbonzini@redhat.com, tglx@linutronix.de, akpm@linux-foundation.org Date: Mon, 04 Feb 2019 15:37:33 -0800 In-Reply-To: <4E64E8CA-6741-47DF-87DE-88D01B01B15D@gmail.com> References: <20190204181118.12095.38300.stgit@localhost.localdomain> <20190204181552.12095.46287.stgit@localhost.localdomain> <4E64E8CA-6741-47DF-87DE-88D01B01B15D@gmail.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: 8bit 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, 2019-02-04 at 15:00 -0800, Nadav Amit wrote: > > On Feb 4, 2019, at 10:15 AM, 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 > > This patch and the following one assume that only KVM should be able to hook > to these events. I do not think it is appropriate for __arch_free_page() to > effectively mean “kvm_guest_free_page()”. > > Is it possible to use the paravirt infrastructure for this feature, > similarly to other PV features? It is not the best infrastructure, but at least > it is hypervisor-neutral. I could probably tie this into the paravirt infrastructure, but if I did so I would probably want to pull the checks for the page order out of the KVM specific bits and make it something we handle in the inline. Doing that I would probably make it a paravirtual hint that only operates at the PMD level. That way we wouldn't incur the cost of the paravirt infrastructure at the per 4K page level.