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[209.132.183.28]) by mx.google.com with ESMTPS id w23si9311941vsq.62.2019.07.24.11.40.06 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 24 Jul 2019 11:40:06 -0700 (PDT) Received-SPF: pass (google.com: domain of nitesh@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 nitesh@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=nitesh@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 1C219308421A; Wed, 24 Jul 2019 18:40:05 +0000 (UTC) Received: from [10.18.17.163] (dhcp-17-163.bos.redhat.com [10.18.17.163]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3BED260BF7; Wed, 24 Jul 2019 18:40:03 +0000 (UTC) Subject: Re: [PATCH v2 0/5] mm / virtio: Provide support for page hinting To: Alexander Duyck , kvm@vger.kernel.org, david@redhat.com, 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> From: Nitesh Narayan Lal Openpgp: preference=signencrypt Autocrypt: addr=nitesh@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190724165158.6685.87228.stgit@localhost.localdomain> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US 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 [10.5.110.40]); Wed, 24 Jul 2019 18:40:05 +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 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 allow= s > for what I am referring to as page hinting > > The functionality for this is fairly simple. When enabled it will alloc= ate > statistics to track the number of hinted pages in a given free area. Wh= en > 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. Th= e > scatterlist is then given to the page hinting device and it will perfor= m > the required action to make the pages "hinted", in the case of > virtio-balloon this results in the pages being madvised as MADV_DONTNEE= D > and as such they are forced out of the guest. After this they are place= d > 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 standa= rd > buddy page. The cycle then repeats with additional non-hinted pages bei= ng > 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 fro= m the hypervisor. > > My primary testing has just been to verify the memory is being freed af= ter > 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 mo= st > of the memory is freed after each iteration. As far as performance I ha= ve > 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 bas= e > kernel without these patches and the patches with virtio-balloon disabl= ed. > 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 f= or > all tests with 8 or more threads.=20 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 memo= ry. 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, howeve= r > I really didn't see a good way to break it up since each piece feeds in= to > 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 o= r > increment/decrement them, or add the Hinted state without something tha= t > 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 previo= us > 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= =2Elocaldomain/ > 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 aer= ated. > Combined size and physical address values in virtio ring into one 64b v= alue. > > 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 c= hanges. As "FREE_PAGE_HINT" and "PAGE_HINTING" are still confusing. > Renamed files and functions from "aeration" to "page_hinting" > Moved from page->lru list to scatterlist > Replaced wait on refcnt in shutdown with RCU and cancel_delayed_work_sy= nc > Virtio now uses scatterlist directly instead of intermedate array > Moved stats out of free_area, now in seperate area and pointed to from = zone > Merged patch 5 into patch 4 to improve reviewability > Updated various code comments throughout > > --- > > Alexander Duyck (5): > mm: Adjust shuffle code to allow for future coalescing > mm: Move set/get_pcppage_migratetype to mmzone.h > mm: Use zone and order instead of free area in free_list manipula= tors > mm: Introduce Hinted pages > virtio-balloon: Add support for providing page hints to host > > > drivers/virtio/Kconfig | 1=20 > drivers/virtio/virtio_balloon.c | 47 ++++++ > include/linux/mmzone.h | 116 ++++++++------ > include/linux/page-flags.h | 8 + > include/linux/page_hinting.h | 139 ++++++++++++++++ > include/uapi/linux/virtio_balloon.h | 1=20 > mm/Kconfig | 5 + > mm/Makefile | 1=20 > mm/internal.h | 18 ++ > mm/memory_hotplug.c | 1=20 > mm/page_alloc.c | 238 ++++++++++++++++++++-------= - > mm/page_hinting.c | 298 +++++++++++++++++++++++++++= ++++++++ > mm/shuffle.c | 24 --- > mm/shuffle.h | 32 ++++ > 14 files changed, 796 insertions(+), 133 deletions(-) > create mode 100644 include/linux/page_hinting.h > create mode 100644 mm/page_hinting.c > > -- --=20 Thanks Nitesh