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Tue, 05 Nov 2019 14:02:01 -0800 (PST) Received: from localhost.localdomain ([2001:470:b:9c3:9e5c:8eff:fe4f:f2d0]) by smtp.gmail.com with ESMTPSA id x70sm25528448pfd.132.2019.11.05.14.02.00 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 05 Nov 2019 14:02:01 -0800 (PST) Subject: [PATCH v13 0/6] mm / virtio: Provide support for unused page reporting From: Alexander Duyck To: 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, david@redhat.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 Date: Tue, 05 Nov 2019 14:02:00 -0800 Message-ID: <20191105215940.15144.65968.stgit@localhost.localdomain> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 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: 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. 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 allocating the non-reported memory and to provide it to the reporting interface via a scatterlist. 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 page is currently unused. It will be faulted back into the guest the next time the page is accessed. To track if a page is reported or not the Uptodate flag was repurposed and used as a Reported flag for Buddy pages. While we are processing the pages in a given zone we have a set of pointers we track called reported_boundary that is used to keep our processing time to a minimum. Without these we would have to iterate through all of the reported pages which would become a significant burden. I measured as much as a 20% performance degradation without using the boundary pointers. In the event of something like compaction needing to process the zone at the same time it currently resorts to resetting the boundary if it is rearranging the list. However in the future it could choose to delay processing the zone if a flag is set indicating that a zone is being actively processed. 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. Test page_fault1 (THP) page_fault2 Baseline 1 1209281.00 +/-0.47% 411314.00 +/-0.42% 16 8804587.33 +/-1.80% 3419453.00 +/-1.80% Patches applied 1 1209369.67 +/-0.06% 412187.00 +/-0.10% 16 8812606.33 +/-0.06% 3435339.33 +/-1.82% Patches enabled 1 1209104.67 +/-0.11% 413067.67 +/-0.43% MADV disabled 16 8835481.67 +/-0.29% 3463485.67 +/-0.50% Patches enabled 1 1210367.67 +/-0.58% 416962.00 +/-0.14% 16 8433236.00 +/-0.58% 3437897.67 +/-0.34% The results above are for a baseline with a linux-next-20191031 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, and the patches applied and page reporting fully enabled. These results include the deviation seen between the average value reported here versus the high and/or low value. I observed that during the test the 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. Most of the overhead seen with this patch set fully enabled is due to the fact that accessing the reported pages will cause a page fault and the host will have to zero the page before giving it back to the guest. The overall guest size is kept fairly small to only a few GB while the test is running. This overhead is much more visible when using THP than with standard 4K pages. As such for the case where the host memory is not oversubscribed this results in a performance regression, however if the host memory were oversubscribed this patch set should result in a performance improvement as swapping memory from the host can be avoided. A brief history on the background of unused page reporting can be found at: https://lore.kernel.org/lkml/29f43d5796feed0dec8e8bb98b187d9dac03b900.camel@linux.intel.com/ Changes from v11: https://lore.kernel.org/lkml/20191001152441.27008.99285.stgit@localhost.localdomain/ Removed unnecessary whitespace change from patch 2 Minor tweak to get_unreported_page to avoid excess writes to boundary Rewrote cover page to lay out additional performance info. Changes from v12: https://lore.kernel.org/lkml/20191022221223.17338.5860.stgit@localhost.localdomain/ 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 --- Alexander Duyck (6): mm: Adjust shuffle code to allow for future coalescing mm: Use zone and order instead of free area in free_list manipulators mm: Introduce Reported pages mm: Add device side and notifier for unused page reporting virtio-balloon: Pull page poisoning config out of free page hinting virtio-balloon: Add support for providing unused page reports to host drivers/virtio/Kconfig | 1 drivers/virtio/virtio_balloon.c | 88 ++++++++- include/linux/mmzone.h | 60 ++---- include/linux/page-flags.h | 11 + include/linux/page_reporting.h | 31 +++ include/uapi/linux/virtio_balloon.h | 1 mm/Kconfig | 11 + mm/Makefile | 1 mm/compaction.c | 5 mm/memory_hotplug.c | 2 mm/page_alloc.c | 199 +++++++++++++++----- mm/page_reporting.c | 353 +++++++++++++++++++++++++++++++++++ mm/page_reporting.h | 226 ++++++++++++++++++++++ mm/shuffle.c | 12 + mm/shuffle.h | 6 + 15 files changed, 905 insertions(+), 102 deletions(-) create mode 100644 include/linux/page_reporting.h create mode 100644 mm/page_reporting.c create mode 100644 mm/page_reporting.h --