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Tue, 26 Nov 2019 12:20:46 +0000 (UTC) Received: from [10.36.118.20] (unknown [10.36.118.20]) by smtp.corp.redhat.com (Postfix) with ESMTP id 776561001DC0; Tue, 26 Nov 2019 12:20:33 +0000 (UTC) Subject: Re: [PATCH v14 0/6] mm / virtio: Provide support for unused page reporting To: Alexander Duyck , kvm@vger.kernel.org, mst@redhat.com, linux-kernel@vger.kernel.org, willy@infradead.org, mhocko@kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, mgorman@techsingularity.net, vbabka@suse.cz Cc: yang.zhang.wz@gmail.com, nitesh@redhat.com, konrad.wilk@oracle.com, pagupta@redhat.com, riel@surriel.com, lcapitulino@redhat.com, dave.hansen@intel.com, wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com, alexander.h.duyck@linux.intel.com, osalvador@suse.de References: <20191119214454.24996.66289.stgit@localhost.localdomain> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAj4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq 7ut6OL64oAq+uQINBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+ xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABiQIl BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl SE+xAvmumFBY Organization: Red Hat GmbH Message-ID: <052f7442-4500-cd02-af2e-56d2f97a232c@redhat.com> Date: Tue, 26 Nov 2019 13:20:32 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191119214454.24996.66289.stgit@localhost.localdomain> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-MC-Unique: 355O7T9NPBSsoMY5TCwDaQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 19.11.19 22:46, Alexander Duyck wrote: > This series provides an asynchronous means of reporting unused guest > pages to a hypervisor so that the memory associated with those pages can > be dropped and reused by other processes and/or guests on the host. Using > this it is possible to avoid unnecessary I/O to disk and greatly improve > performance in the case of memory overcommit on the host. >=20 > When enabled it will allocate a set of statistics to track the number of > reported pages. When the nr_free for a given free area is greater than > this by the high water mark we will schedule a worker to begin pulling th= e > non-reported memory and to provide it to the reporting interface via a > scatterlist. >=20 > Currently this is only in use by virtio-balloon however there is the hope > that at some point in the future other hypervisors might be able to make > use of it. In the virtio-balloon/QEMU implementation the hypervisor is > currently using MADV_DONTNEED to indicate to the host kernel that the pag= e > is currently unused. It will be zeroed and faulted back into the guest th= e > next time the page is accessed. Remind me why we are using MADV_DONTNEED? Mostly for debugging purposes right now, right? Did you do any measurements with MADV_FREE? I guess there should be quite a performance increase in some scenarios. >=20 > To track if a page is reported or not the Uptodate flag was repurposed an= d > used as a Reported flag for Buddy pages. We walk though the free list > isolating pages and adding them to the scatterlist until we either > encounter the end of the list or have filled the scatterlist with pages t= o > be reported. If we fill the scatterlist before we reach the end of the > list we rotate the list so that the first unreported page we encounter is > moved to the head of the list as that is where we will resume after we > have freed the reported pages back into the tail of the list. So the boundary pointer didn't actually provide that big of a benefit I assume (IOW, worst thing is you have to re-scan the whole list)? >=20 > Below are the results from various benchmarks. I primarily focused on two > tests. The first is the will-it-scale/page_fault2 test, and the other is > a modified version of will-it-scale/page_fault1 that was enabled to use > THP. I did this as it allows for better visibility into different parts > of the memory subsystem. The guest is running with 32G for RAM on one > node of a E5-2630 v3. The host has had some power saving features disable= d > by setting the /dev/cpu_dma_latency value to 10ms. >=20 > Test page_fault1 (THP) page_fault2 > Name tasks Process Iter STDEV Process Iter STDEV > Baseline 1 1203934.75 0.04% 379940.75 0.11% > 16 8828217.00 0.85% 3178653.00 1.28% >=20 > Patches applied 1 1207961.25 0.10% 380852.25 0.25% > 16 8862373.00 0.98% 3246397.25 0.68% >=20 > Patches enabled 1 1207758.75 0.17% 373079.25 0.60% > MADV disabled 16 8870373.75 0.29%=09 3204989.75 1.08% >=20 > Patches enabled 1 1261183.75 0.39% 373201.50 0.50% > 16 8371359.75 0.65% 3233665.50 0.84% >=20 > Patches enabled 1 1090201.50 0.25% 376967.25 0.29% > page shuffle 16 8108719.75 0.58% 3218450.25 1.07% >=20 > The results above are for a baseline with a linux-next-20191115 kernel, > that kernel with this patch set applied but page reporting disabled in > virtio-balloon, patches applied but the madvise disabled by direct > assigning a device, the patches applied and page reporting fully > enabled, and the patches enabled with page shuffling enabled. These > results include the deviation seen between the average value reported her= e > versus the high and/or low value. I observed that during the test memory > usage for the first three tests never dropped whereas with the patches > fully enabled the VM would drop to using only a few GB of the host's > memory when switching from memhog to page fault tests. >=20 > Most of the overhead seen with this patch set enabled seems due to page > faults caused by accessing the reported pages and the host zeroing the pa= ge > before giving it back to the guest. This overhead is much more visible wh= en > using THP than with standard 4K pages. In addition page shuffling seemed = to > increase the amount of faults generated due to an increase in memory chur= n. MADV_FREE would be interesting. >=20 > The overall guest size is kept fairly small to only a few GB while the te= st > is running. If the host memory were oversubscribed this patch set should > result in a performance improvement as swapping memory in the host can be > avoided. >=20 > A brief history on the background of unused page reporting can be found a= t: > https://lore.kernel.org/lkml/29f43d5796feed0dec8e8bb98b187d9dac03b900.cam= el@linux.intel.com/ >=20 > Changes from v12: > https://lore.kernel.org/lkml/20191022221223.17338.5860.stgit@localhost.lo= caldomain/ > Rebased on linux-next 20191031 > Renamed page_is_reported to page_reported > Renamed add_page_to_reported_list to mark_page_reported > Dropped unused definition of add_page_to_reported_list for non-reporting = case > Split free_area_reporting out from get_unreported_tail > Minor updates to cover page >=20 > Changes from v13: > https://lore.kernel.org/lkml/20191105215940.15144.65968.stgit@localhost.l= ocaldomain/ > Rewrote core reporting functionality > Merged patches 3 & 4 > Dropped boundary list and related code > Folded get_reported_page into page_reporting_fill > Folded page_reporting_fill into page_reporting_cycle > Pulled reporting functionality out of free_reported_page > Renamed it to __free_isolated_page > Moved page reporting specific bits to page_reporting_drain > Renamed phdev to prdev since we aren't "hinting" we are "reporting" > Added documentation to describe the usage of unused page reporting > Updated cover page and patch descriptions to avoid mention of boundary >=20 >=20 > --- >=20 > Alexander Duyck (6): > mm: Adjust shuffle code to allow for future coalescing > mm: Use zone and order instead of free area in free_list manipulato= rs > mm: Introduce Reported pages > mm: Add unused page reporting documentation > virtio-balloon: Pull page poisoning config out of free page hinting > virtio-balloon: Add support for providing unused page reports to ho= st >=20 >=20 > Documentation/vm/unused_page_reporting.rst | 44 ++++ > drivers/virtio/Kconfig | 1=20 > drivers/virtio/virtio_balloon.c | 88 +++++++ > include/linux/mmzone.h | 56 +---- > include/linux/page-flags.h | 11 + > include/linux/page_reporting.h | 31 +++ > include/uapi/linux/virtio_balloon.h | 1=20 > mm/Kconfig | 11 + > mm/Makefile | 1=20 > mm/memory_hotplug.c | 2=20 > mm/page_alloc.c | 181 +++++++++++---- > mm/page_reporting.c | 337 ++++++++++++++++++++++= ++++++ > mm/page_reporting.h | 125 ++++++++++ > mm/shuffle.c | 12 - > mm/shuffle.h | 6=20 > 15 files changed, 805 insertions(+), 102 deletions(-) So roughly 100 LOC less added, that's nice to see :) I'm planning to look into the details soon, just fairly busy lately. I hope Mel Et al. can also comment. --=20 Thanks, David / dhildenb