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Tue, 27 Nov 2018 15:20:40 -0500 Received: from mx2.suse.de ([195.135.220.15]:45348 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729971AbeK0UUj (ORCPT ); Tue, 27 Nov 2018 15:20:39 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C1227AF8D; Tue, 27 Nov 2018 09:23:21 +0000 (UTC) Subject: Re: [PATCH 4/5] mm: Reclaim small amounts of memory when an external fragmentation event occurs To: Mel Gorman , Andrew Morton Cc: David Rientjes , Andrea Arcangeli , Zi Yan , Michal Hocko , LKML , Linux-MM References: <20181123114528.28802-1-mgorman@techsingularity.net> <20181123114528.28802-5-mgorman@techsingularity.net> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSFWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmNvbT7CwZcEEwEKAEECGwMFCwkIBwMFFQoJCAsFFgIDAQAC HgECF4ACGQEWIQSpQNQ0mSwujpkQPVAiT6fnzIKmZAUCWi/zTwUJBbOLuQAKCRAiT6fnzIKm ZIpED/4jRN/6LKZZIT4R2xoou0nJkBGVA3nfb+mUMgi3uwn/zC+o6jjc3ShmP0LQ0cdeuSt/ t2ytstnuARTFVqZT4/IYzZgBsLM8ODFY5vGfPw00tsZMIfFuVPQX3xs0XgLEHw7/1ZCVyJVr mTzYmV3JruwhMdUvIzwoZ/LXjPiEx1MRdUQYHAWwUfsl8lUZeu2QShL3KubR1eH6lUWN2M7t VcokLsnGg4LTajZzZfq2NqCKEQMY3JkAmOu/ooPTrfHCJYMF/5dpi8YF1CkQF/PVbnYbPUuh dRM0m3NzPtn5DdyfFltJ7fobGR039+zoCo6dFF9fPltwcyLlt1gaItfX5yNbOjX3aJSHY2Vc A5T+XAVC2sCwj0lHvgGDz/dTsMM9Ob/6rRJANlJPRWGYk3WVWnbgW8UejCWtn1FkiY/L/4qJ UsqkId8NkkVdVAenCcHQmOGjRQYTpe6Cf4aQ4HGNDeWEm3H8Uq9vmHhXXcPLkxBLRbGDSHyq vUBVaK+dAwAsXn/5PlGxw1cWtur1ep7RDgG3vVQDhIOpAXAg6HULjcbWpBEFaoH720oyGmO5 kV+yHciYO3nPzz/CZJzP5Ki7Q1zqBb/U6gib2at5Ycvews+vTueYO+rOb9sfD8BFTK386LUK uce7E38owtgo/V2GV4LMWqVOy1xtCB6OAUfnGDU2EM7ATQRbGTU1AQgAn0H6UrFiWcovkh6E XVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQLa1PQDUi6j00ChlcR66g9/V0sPIcSutacPKf dKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMhFmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCT sTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sfbAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZO rIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq+aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahK tQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4njQARAQABwsF8BBgBCgAmFiEEqUDUNJksLo6Z ED1QIk+n58yCpmQFAlsZNTUCGwwFCQPCZwAACgkQIk+n58yCpmQ83g/9Frg1sRMdGPn98zV+ O2eC3h0p5f/oxxQ8MhG5znwHoW4JDG2TuxfcQuz7X7Dd5JWscjlw4VFJ2DD+IrDAGLHwPhCr RyfKalnrbYokvbClM9EuU1oUuh7k+Sg5ECNXEsamW9AiWGCaKWNDdHre3Lf4xl+RJWxghOVW RiUdpLA/a3yDvJNVr6rxkDHQ1P24ZZz/VKDyP+6g8aty2aWEU0YFNjI+rqYZb2OppDx6fdma YnLDcIfDFnkVlDmpznnGCyEqLLyMS3GH52AH13zMT9L9QYgT303+r6QQpKBIxAwn8Jg8dAlV OLhgeHXKr+pOQdFf6iu2sXlUR4MkO/5KWM1K0jFR2ug8Pb3aKOhowVMBT64G0TXhQ/kX4tZ2 ZF0QZLUCHU3Cigvbu4AWWVMNDEOGD/4sn9OoHxm6J04jLUHFUpFKDcjab4NRNWoHLsuLGjve Gdbr2RKO2oJ5qZj81K7os0/5vTAA4qHDP2EETAQcunTn6aPlkUnJ8aw6I1Rwyg7/XsU7gQHF IM/cUMuWWm7OUUPtJeR8loxZiZciU7SMvN1/B9ycPMFs/A6EEzyG+2zKryWry8k7G/pcPrFx O2PkDPy3YmN1RfpIX2HEmnCEFTTCsKgYORangFu/qOcXvM83N+2viXxG4mjLAMiIml1o2lKV cqmP8roqufIAj+Ohhzs= Message-ID: <0e042569-eb95-623f-242c-9cf9c87c5223@suse.cz> Date: Tue, 27 Nov 2018 10:23:21 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: <20181123114528.28802-5-mgorman@techsingularity.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/23/18 12:45 PM, Mel Gorman wrote: > An external fragmentation event was previously described as > > When the page allocator fragments memory, it records the event using > the mm_page_alloc_extfrag event. If the fallback_order is smaller > than a pageblock order (order-9 on 64-bit x86) then it's considered > an event that will cause external fragmentation issues in the future. > > The kernel reduces the probability of such events by increasing the > watermark sizes by calling set_recommended_min_free_kbytes early in the > lifetime of the system. This works reasonably well in general but if there > are enough sparsely populated pageblocks then the problem can still occur > as enough memory is free overall and kswapd stays asleep. > > This patch introduces a watermark_boost_factor sysctl that allows a zone > watermark to be temporarily boosted when an external fragmentation causing > events occurs. The boosting will stall allocations that would decrease > free memory below the boosted low watermark and kswapd is woken if the > calling context allows to reclaim an amount of memory relative to the > size of the high watermark and the watermark_boost_factor until the boost > is cleared. When kswapd finishes, it wakes kcompactd at the pageblock > order to clean some of the pageblocks that may have been affected by > the fragmentation event. kswapd avoids any writeback, slab shrinkage and > swap from reclaim context during this operation to avoid excessive system > disruption in the name of fragmentation avoidance. Care is taken so that > kswapd will do normal reclaim work if the system is really low on memory. > > This was evaluated using the same workloads as "mm, page_alloc: Spread > allocations across zones before introducing fragmentation". > > 1-socket Skylake machine > config-global-dhp__workload_thpfioscale XFS (no special madvise) > 4 fio threads, 1 THP allocating thread > -------------------------------------- > > 4.20-rc3 extfrag events < order 9: 804694 > 4.20-rc3+patch: 408912 (49% reduction) > 4.20-rc3+patch1-4: 18421 (98% reduction) > > 4.20.0-rc3 4.20.0-rc3 > lowzone-v5r8 boost-v5r8 > Amean fault-base-1 653.58 ( 0.00%) 652.71 ( 0.13%) > Amean fault-huge-1 0.00 ( 0.00%) 178.93 * -99.00%* > > 4.20.0-rc3 4.20.0-rc3 > lowzone-v5r8 boost-v5r8 > Percentage huge-1 0.00 ( 0.00%) 5.12 ( 100.00%) > > Note that external fragmentation causing events are massively reduced > by this path whether in comparison to the previous kernel or the vanilla > kernel. The fault latency for huge pages appears to be increased but that > is only because THP allocations were successful with the patch applied. > > 1-socket Skylake machine > global-dhp__workload_thpfioscale-madvhugepage-xfs (MADV_HUGEPAGE) > ----------------------------------------------------------------- > > 4.20-rc3 extfrag events < order 9: 291392 > 4.20-rc3+patch: 191187 (34% reduction) > 4.20-rc3+patch1-4: 13464 (95% reduction) > > thpfioscale Fault Latencies > 4.20.0-rc3 4.20.0-rc3 > lowzone-v5r8 boost-v5r8 > Min fault-base-1 912.00 ( 0.00%) 905.00 ( 0.77%) > Min fault-huge-1 127.00 ( 0.00%) 135.00 ( -6.30%) > Amean fault-base-1 1467.55 ( 0.00%) 1481.67 ( -0.96%) > Amean fault-huge-1 1127.11 ( 0.00%) 1063.88 * 5.61%* > > 4.20.0-rc3 4.20.0-rc3 > lowzone-v5r8 boost-v5r8 > Percentage huge-1 77.64 ( 0.00%) 83.46 ( 7.49%) > > As before, massive reduction in external fragmentation events, some jitter > on latencies and an increase in THP allocation success rates. > > 2-socket Haswell machine > config-global-dhp__workload_thpfioscale XFS (no special madvise) > 4 fio threads, 5 THP allocating threads > ---------------------------------------------------------------- > > 4.20-rc3 extfrag events < order 9: 215698 > 4.20-rc3+patch: 200210 (7% reduction) > 4.20-rc3+patch1-4: 14263 (93% reduction) > > 4.20.0-rc3 4.20.0-rc3 > lowzone-v5r8 boost-v5r8 > Amean fault-base-5 1346.45 ( 0.00%) 1306.87 ( 2.94%) > Amean fault-huge-5 3418.60 ( 0.00%) 1348.94 ( 60.54%) > > 4.20.0-rc3 4.20.0-rc3 > lowzone-v5r8 boost-v5r8 > Percentage huge-5 0.78 ( 0.00%) 7.91 ( 910.64%) > > There is a 93% reduction in fragmentation causing events, there > is a big reduction in the huge page fault latency and allocation > success rate is higher. > > 2-socket Haswell machine > global-dhp__workload_thpfioscale-madvhugepage-xfs (MADV_HUGEPAGE) > ----------------------------------------------------------------- > > 4.20-rc3 extfrag events < order 9: 166352 > 4.20-rc3+patch: 147463 (11% reduction) > 4.20-rc3+patch1-4: 11095 (93% reduction) > > thpfioscale Fault Latencies > 4.20.0-rc3 4.20.0-rc3 > lowzone-v5r8 boost-v5r8 > Amean fault-base-5 6217.43 ( 0.00%) 7419.67 * -19.34%* > Amean fault-huge-5 3163.33 ( 0.00%) 3263.80 ( -3.18%) > > 4.20.0-rc3 4.20.0-rc3 > lowzone-v5r8 boost-v5r8 > Percentage huge-5 95.14 ( 0.00%) 87.98 ( -7.53%) > > There is a large reduction in fragmentation events with some jitter around > the latencies and success rates. As before, the high THP allocation > success rate does mean the system is under a lot of pressure. However, > as the fragmentation events are reduced, it would be expected that the > long-term allocation success rate would be higher. > > Signed-off-by: Mel Gorman Acked-by: Vlastimil Babka