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[209.132.183.28]) by mx.google.com with ESMTPS id v20si30257022qvf.203.2019.07.24.11.41.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 24 Jul 2019 11:41:52 -0700 (PDT) Received-SPF: pass (google.com: domain of david@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 david@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9C27B30C0DCF; Wed, 24 Jul 2019 18:41:51 +0000 (UTC) Received: from [10.36.116.35] (ovpn-116-35.ams2.redhat.com [10.36.116.35]) by smtp.corp.redhat.com (Postfix) with ESMTP id C234260BF7; Wed, 24 Jul 2019 18:41:34 +0000 (UTC) Subject: Re: [PATCH v2 0/5] mm / virtio: Provide support for page hinting To: Nitesh Narayan Lal , Alexander Duyck , kvm@vger.kernel.org, mst@redhat.com, dave.hansen@intel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org Cc: yang.zhang.wz@gmail.com, pagupta@redhat.com, riel@surriel.com, konrad.wilk@oracle.com, lcapitulino@redhat.com, wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com, alexander.h.duyck@linux.intel.com References: <20190724165158.6685.87228.stgit@localhost.localdomain> <0c520470-4654-cdf2-cf4d-d7c351d25e8b@redhat.com> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <0c520470-4654-cdf2-cf4d-d7c351d25e8b@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Wed, 24 Jul 2019 18:41:51 +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 24.07.19 20:40, Nitesh Narayan Lal wrote: > > On 7/24/19 12:54 PM, Alexander Duyck wrote: >> This series provides an asynchronous means of hinting to a hypervisor >> that a guest page is no longer in use and can have the data associated >> with it dropped. To do this I have implemented functionality that allows >> for what I am referring to as page hinting >> >> The functionality for this is fairly simple. When enabled it will allocate >> statistics to track the number of hinted pages in a given free area. When >> the number of free pages exceeds this value plus a high water value, >> currently 32, > Shouldn't we configure this to a lower number such as 16? >> it will begin performing page hinting which consists of >> pulling pages off of free list and placing them into a scatter list. The >> scatterlist is then given to the page hinting device and it will perform >> the required action to make the pages "hinted", in the case of >> virtio-balloon this results in the pages being madvised as MADV_DONTNEED >> and as such they are forced out of the guest. After this they are placed >> back on the free list, and an additional bit is added if they are not >> merged indicating that they are a hinted buddy page instead of a standard >> buddy page. The cycle then repeats with additional non-hinted pages being >> pulled until the free areas all consist of hinted pages. >> >> I am leaving a number of things hard-coded such as limiting the lowest >> order processed to PAGEBLOCK_ORDER, > Have you considered making this option configurable at the compile time? >> and have left it up to the guest to >> determine what the limit is on how many pages it wants to allocate to >> process the hints. > It might make sense to set the number of pages to be hinted at a time from the > hypervisor. >> >> My primary testing has just been to verify the memory is being freed after >> allocation by running memhog 79g on a 80g guest and watching the total >> free memory via /proc/meminfo on the host. With this I have verified most >> of the memory is freed after each iteration. As far as performance I have >> been mainly focusing on the will-it-scale/page_fault1 test running with >> 16 vcpus. With that I have seen at most a 2% difference between the base >> kernel without these patches and the patches with virtio-balloon disabled. >> With the patches and virtio-balloon enabled with hinting the results >> largely depend on the host kernel. On a 3.10 RHEL kernel I saw up to a 2% >> drop in performance as I approached 16 threads, > I think this is acceptable. >> however on the the lastest >> linux-next kernel I saw roughly a 4% to 5% improvement in performance for >> all tests with 8 or more threads. > Do you mean that with your patches the will-it-scale/page_fault1 numbers were > better by 4-5% over an unmodified kernel? >> I believe the difference seen is due to >> the overhead for faulting pages back into the guest and zeroing of memory. > It may also make sense to test these patches with netperf to observe how much > performance drop it is introducing. >> Patch 4 is a bit on the large side at about 600 lines of change, however >> I really didn't see a good way to break it up since each piece feeds into >> the next. So I couldn't add the statistics by themselves as it didn't >> really make sense to add them without something that will either read or >> increment/decrement them, or add the Hinted state without something that >> would set/unset it. As such I just ended up adding the entire thing as >> one patch. It makes it a bit bigger but avoids the issues in the previous >> set where I was referencing things before they had been added. >> >> Changes from the RFC: >> https://lore.kernel.org/lkml/20190530215223.13974.22445.stgit@localhost.localdomain/ >> Moved aeration requested flag out of aerator and into zone->flags. >> Moved bounary out of free_area and into local variables for aeration. >> Moved aeration cycle out of interrupt and into workqueue. >> Left nr_free as total pages instead of splitting it between raw and aerated. >> Combined size and physical address values in virtio ring into one 64b value. >> >> Changes from v1: >> https://lore.kernel.org/lkml/20190619222922.1231.27432.stgit@localhost.localdomain/ >> Dropped "waste page treatment" in favor of "page hinting" > We may still have to try and find a better name for virtio-balloon side changes. > As "FREE_PAGE_HINT" and "PAGE_HINTING" are still confusing. We should have named that free page reporting, but that train already has left. -- Thanks, David / dhildenb