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[46.22.139.17]) by mx.google.com with ESMTPS id m5si583875edv.193.2018.11.07.10.38.23 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 07 Nov 2018 10:38:23 -0800 (PST) Received-SPF: pass (google.com: domain of mgorman@techsingularity.net designates 46.22.139.17 as permitted sender) client-ip=46.22.139.17; Authentication-Results: mx.google.com; spf=pass (google.com: domain of mgorman@techsingularity.net designates 46.22.139.17 as permitted sender) smtp.mailfrom=mgorman@techsingularity.net Received: from mail.blacknight.com (pemlinmail06.blacknight.ie [81.17.255.152]) by outbound-smtp12.blacknight.com (Postfix) with ESMTPS id 643051C1E17 for ; Wed, 7 Nov 2018 18:38:23 +0000 (GMT) Received: (qmail 19783 invoked from network); 7 Nov 2018 18:38:23 -0000 Received: from unknown (HELO stampy.163woodhaven.lan) (mgorman@techsingularity.net@[37.228.229.69]) by 81.17.254.9 with ESMTPA; 7 Nov 2018 18:38:23 -0000 From: Mel Gorman To: Linux-MM Cc: Andrew Morton , Vlastimil Babka , David Rientjes , Andrea Arcangeli , Zi Yan , LKML , Mel Gorman Subject: [PATCH 0/5] Fragmentation avoidance improvements v2 Date: Wed, 7 Nov 2018 18:38:17 +0000 Message-Id: <20181107183822.15567-1-mgorman@techsingularity.net> X-Mailer: git-send-email 2.16.4 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: X-Virus-Scanned: ClamAV using ClamSMTP The 1-socket machine is different to the one used in v1 so some of the results are changed on that basis. The baseline has changed to 4.20-rc1 so the __GFP_THISNODE removal for THP is in effect which alters the behaviour on 2-socket in particular. The biggest changes are in the fourth patch, both in terms of functional changes and the fact it adds a vmstat and tracepoint for measuring stall latency. Changelog since v1 o Rebase to v4.20-rc1 for the THP __GFP_THISNODE patch in particular o Add tracepoint to record fragmentation stall durations o Add vmstat event to record that a fragmentation stall occurred o Stalls now alter watermark boosting o Stalls occur only when the allocation is about to fail It has been noted before that fragmentation avoidance (aka anti-fragmentation) is not perfect. Given sufficient time or an adverse workload, memory gets fragmented and the long-term success of high-order allocations degrades. This series defines an adverse workload, a definition of external fragmentation events (including serious) ones and a series that reduces the level of those fragmentation events. The details of the workload and the consequences are described in more detail in the changelogs. However, from patch 1, this is a high-level summary of the adverse workload. The exact details are found in the mmtests implementation. The broad details of the workload are as follows; 1. Create an XFS filesystem (not specified in the configuration but done as part of the testing for this patch) 2. Start 4 fio threads that write a number of 64K files inefficiently. Inefficiently means that files are created on first access and not created in advance (fio parameterr create_on_open=1) and fallocate is not used (fallocate=none). With multiple IO issuers this creates a mix of slab and page cache allocations over time. The total size of the files is 150% physical memory so that the slabs and page cache pages get mixed 3. Warm up a number of fio read-only threads accessing the same files created in step 2. This part runs for the same length of time it took to create the files. It'll fault back in old data and further interleave slab and page cache allocations. As it's now low on memory due to step 2, fragmentation occurs as pageblocks get stolen. 4. While step 3 is still running, start a process that tries to allocate 75% of memory as huge pages with a number of threads. The number of threads is based on a (NR_CPUS_SOCKET - NR_FIO_THREADS)/4 to avoid THP threads contending with fio, any other threads or forcing cross-NUMA scheduling. Note that the test has not been used on a machine with less than 8 cores. The benchmark records whether huge pages were allocated and what the fault latency was in microseconds 5. Measure the number of events potentially causing external fragmentation, the fault latency and the huge page allocation success rate. 6. Cleanup Overall the series reduces external fragmentation causing events by over 95% on 1 and 2 socket machines, which in turn impacts high-order allocation success rates over the long term. There are differences in latencies and high-order allocation success rates. Latencies are a mixed bag as they are vulnerable to exact system state and whether allocations succeeded so they are treated as a secondary metric. Patch 1 uses lower zones if they are populated and have free memory instead of fragmenting a higher zone. It's special cased to handle a Normal->DMA32 fallback with the reasons explained in the changelog. Patch 2+3 boosts watermarks temporarily when an external fragmentation event occurs. kswapd wakes to reclaim a small amount of old memory and then wakes kcompactd on completion to recover the system slightly. This introduces some overhead in the slowpath. The level of boosting can be tuned or disabled depending on the tolerance for fragmentation vs allocation latency. Patch 4 is more heavy handed. In the event of a movable allocation request that can stall, it'll wake kswapd as in patch 3. However, if the expected fragmentation event is serious then the request will stall briefly on pfmemalloc_wait until kswapd completes light reclaim work and retry the allocation without stalling. This can avoid the fragmentation event entirely in some cases. The definition of a serious fragmentation event can be tuned or disabled. Patch 5 is the hardest to prove it's a real benefit. In the event that fragmentation was unavoidable, it'll queue a pageblock for kcompactd to clean. It's a fixed-length queue that is neither guaranteed to have a slot available or successfully clean a pageblock. Patches 4 and 5 can be treated independently or dropped if necessary. This is particularly true of patch 5 as the benefit is difficult to detect given the impact of the first 4 patches. The bulk of the improvement in fragmentation avoidance is from patches 1-3 (94-97% reduction in fragmentation events for an adverse workload on both a 1-socket and 2-socket machine). The primary benefit of patch 4 is the increase in THP success rates and the fact it reduces fragmentation events to almost negligible levels with the option of eliminating them. Documentation/sysctl/vm.txt | 42 +++++++ include/linux/compaction.h | 4 + include/linux/migrate.h | 7 +- include/linux/mm.h | 2 + include/linux/mmzone.h | 18 ++- include/linux/vm_event_item.h | 1 + include/trace/events/compaction.h | 62 ++++++++++ include/trace/events/kmem.h | 21 ++++ kernel/sysctl.c | 18 +++ mm/compaction.c | 147 +++++++++++++++++++++-- mm/internal.h | 14 ++- mm/migrate.c | 6 +- mm/page_alloc.c | 246 ++++++++++++++++++++++++++++++++++---- mm/vmscan.c | 123 +++++++++++++++++-- mm/vmstat.c | 1 + 15 files changed, 661 insertions(+), 51 deletions(-)