From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nitesh Narayan Lal Subject: Re: [RFC PATCH 0/4] kvm: Report unused guest pages to host Date: Thu, 7 Feb 2019 09:48:27 -0500 Message-ID: References: <20190204181118.12095.38300.stgit@localhost.localdomain> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="u3whL6aquCy1ts4iceBw9JljlbrMn7YPA" Cc: 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, Luiz Capitulino , David Hildenbrand To: Alexander Duyck , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Return-path: In-Reply-To: <20190204181118.12095.38300.stgit@localhost.localdomain> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --u3whL6aquCy1ts4iceBw9JljlbrMn7YPA Content-Type: multipart/mixed; boundary="DOAx8TQ4zzvecILyQ2LYNZmFYya6XHM3o"; protected-headers="v1" From: Nitesh Narayan Lal To: Alexander Duyck , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: 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, Luiz Capitulino , David Hildenbrand Message-ID: Subject: Re: [RFC PATCH 0/4] kvm: Report unused guest pages to host References: <20190204181118.12095.38300.stgit@localhost.localdomain> In-Reply-To: <20190204181118.12095.38300.stgit@localhost.localdomain> --DOAx8TQ4zzvecILyQ2LYNZmFYya6XHM3o Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US On 2/4/19 1:15 PM, Alexander Duyck wrote: > This patch set provides a mechanism by which guests can notify the host= of > pages that are not currently in use. Using this data a KVM host can mor= e > easily balance memory workloads between guests and improve overall syst= em > performance by avoiding unnecessary writing of unused pages to swap. > > In order to support this I have added a new hypercall to provided unuse= d > page hints and made use of mechanisms currently used by PowerPC and s39= 0 > architectures to provide those hints. To reduce the overhead of this ca= ll > I am only using it per huge page instead of of doing a notification per= 4K > page. By doing this we can avoid the expense of fragmenting higher orde= r > pages, and reduce overall cost for the hypercall as it will only be > performed once per huge page. > > Because we are limiting this to huge pages it was necessary to add a > secondary location where we make the call as the buddy allocator can me= rge > smaller pages into a higher order huge page. > > This approach is not usable in all cases. Specifically, when KVM direct= > device assignment is used, the memory for a guest is permanently assign= ed > to physical pages in order to support DMA from the assigned device. In > this case we cannot give the pages back, so the hypercall is disabled b= y > the host. > > Another situation that can lead to issues is if the page were accessed > immediately after free. For example, if page poisoning is enabled the > guest will populate the page *after* freeing it. In this case it does n= ot > make sense to provide a hint about the page being freed so we do not > perform the hypercalls from the guest if this functionality is enabled.= Hi Alexander, Did you get a chance to look at my v8 posting of Guest Free Page Hinting [1]? Considering both the solutions are trying to solve the same problem. It will be great if we can collaborate and come up with a unified solution. [1] https://lkml.org/lkml/2019/2/4/993 > > My testing up till now has consisted of setting up 4 8GB VMs on a syste= m > with 32GB of memory and 4GB of swap. To stress the memory on the system= I > would run "memhog 8G" sequentially on each of the guests and observe ho= w > long it took to complete the run. The observed behavior is that on the > systems with these patches applied in both the guest and on the host I = was > able to complete the test with a time of 5 to 7 seconds per guest. On a= > system without these patches the time ranged from 7 to 49 seconds per > guest. I am assuming the variability is due to time being spent writing= > pages out to disk in order to free up space for the guest. > > --- > > Alexander Duyck (4): > madvise: Expose ability to set dontneed from kernel > kvm: Add host side support for free memory hints > kvm: Add guest side support for free memory hints > mm: Add merge page notifier > > > Documentation/virtual/kvm/cpuid.txt | 4 ++ > Documentation/virtual/kvm/hypercalls.txt | 14 ++++++++ > arch/x86/include/asm/page.h | 25 +++++++++++++++ > arch/x86/include/uapi/asm/kvm_para.h | 3 ++ > arch/x86/kernel/kvm.c | 51 ++++++++++++++++++++++= ++++++++ > arch/x86/kvm/cpuid.c | 6 +++- > arch/x86/kvm/x86.c | 35 +++++++++++++++++++++ > include/linux/gfp.h | 4 ++ > include/linux/mm.h | 2 + > include/uapi/linux/kvm_para.h | 1 + > mm/madvise.c | 13 +++++++- > mm/page_alloc.c | 2 + > 12 files changed, 158 insertions(+), 2 deletions(-) > > -- --=20 Regards Nitesh --DOAx8TQ4zzvecILyQ2LYNZmFYya6XHM3o-- --u3whL6aquCy1ts4iceBw9JljlbrMn7YPA Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEkXcoRVGaqvbHPuAGo4ZA3AYyozkFAlxcRTsACgkQo4ZA3AYy oznkYBAAxlLH2s8HfygIKMiuKDu6CPvf/Fk18SRuvBRIFJSSOyeC/qzlDoyn8By6 tLRTpm7sAnrU1eCzfKq2GUSWrFPxAIHVe1ynU/gpaqE16ynC6TjENlSNeCyHUC1P r8QD5E+aNa2hIbkNcBmiMvS3a9fPJo9FyoWdY0S8hqABvpDMJ1r3E5Rawnrfw8EX qadktlGMdMRcyv9xepwf75fc7eRQmTHdXTJcUn0svqQTL89F6IZ4uXJmkfMtL9Gn 7tVEbghXQlDuUaVQ8NgZwn0M2o5wg/PyC3mTX2kJL90Pi5uEX8/tNrRh/bay3o0Y izULYHVm4LizCGDtRoT6zX8N6lG/+VtO4FIaO+rcmhb1La4UCGTlZ/BToe/rH1+W Uy5FpfxmgrpJJ4S2/15lPUIXeAM4XlZjqqX0lHW8o0+cd4fQ3PsmjWQPPL6oIYAT L8vwgD80lUFvTi0Lvn8nWtXynTPH0Re8PVh3sP8GA0tiCtuDaYRGSblUHEjf5z1a KqpfSl+dq2IcQjAUd8Y34FKS/KSzRsNa1hseCr2aImWdpgrz2gQr6Q1rqmV0YXSg x4GDPp+syLtPdg200l+AJ/oPzg6heu+zVf83zn4m7O5W6pH71aIwS8sL5PLLjF2K mwpz4LNGlhuPey8ruTnnS4BZiV4kXSiUJOjFZZ2ZwYJvrccHFZI= =H1K3 -----END PGP SIGNATURE----- --u3whL6aquCy1ts4iceBw9JljlbrMn7YPA--