From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: + mm-vmscan-dont-round-up-scan-size-for-online-memory-cgroup.patch added to -mm tree Date: Thu, 13 Feb 2020 21:22:28 -0800 Message-ID: <20200214052228.qry-CKsYL%akpm@linux-foundation.org> References: <20200203173311.6269a8be06a05e5a4aa08a93@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:48760 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725775AbgBNFWb (ORCPT ); Fri, 14 Feb 2020 00:22:31 -0500 In-Reply-To: <20200203173311.6269a8be06a05e5a4aa08a93@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: gshan@redhat.com, guro@fb.com, mm-commits@vger.kernel.org, stable@vger.kernel.org The patch titled Subject: mm/vmscan.c: don't round up scan size for online memory cgroup has been added to the -mm tree. Its filename is mm-vmscan-dont-round-up-scan-size-for-online-memory-cgroup.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-vmscan-dont-round-up-scan-size-for-online-memory-cgroup.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-vmscan-dont-round-up-scan-size-for-online-memory-cgroup.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Gavin Shan Subject: mm/vmscan.c: don't round up scan size for online memory cgroup commit 68600f623d69 ("mm: don't miss the last page because of round-off error") makes the scan size round up to @denominator regardless of the memory cgroup's state, online or offline. This affects the overall reclaiming behavior: The corresponding LRU list is eligible for reclaiming only when its size logically right shifted by @sc->priority is bigger than zero in the former formula. For example, the inactive anonymous LRU list should have at least 0x4000 pages to be eligible for reclaiming when we have 60/12 for swappiness/priority and without taking scan/rotation ratio into account. After the roundup is applied, the inactive anonymous LRU list becomes eligible for reclaiming when its size is bigger than or equal to 0x1000 in the same condition. (0x4000 >> 12) * 60 / (60 + 140 + 1) = 1 ((0x1000 >> 12) * 60) + 200) / (60 + 140 + 1) = 1 aarch64 has 512MB huge page size when the base page size is 64KB. The memory cgroup that has a huge page is always eligible for reclaiming in that case. The reclaiming is likely to stop after the huge page is reclaimed, meaing the further iteration on @sc->priority and the silbing and child memory cgroups will be skipped. The overall behaviour has been changed. This fixes the issue by applying the roundup to offlined memory cgroups only, to give more preference to reclaim memory from offlined memory cgroup. It sounds reasonable as those memory is unlikedly to be used by anyone. The issue was found by starting up 8 VMs on a Ampere Mustang machine, which has 8 CPUs and 16 GB memory. Each VM is given with 2 vCPUs and 2GB memory. It took 264 seconds for all VMs to be completely up and 784MB swap is consumed after that. With this patch applied, it took 236 seconds and 60MB swap to do same thing. So there is 10% performance improvement for my case. Note that KSM is disable while THP is enabled in the testing. total used free shared buff/cache available Mem: 16196 10065 2049 16 4081 3749 Swap: 8175 784 7391 total used free shared buff/cache available Mem: 16196 11324 3656 24 1215 2936 Swap: 8175 60 8115 Link: http://lkml.kernel.org/r/20200211024514.8730-1-gshan@redhat.com Fixes: 68600f623d69 ("mm: don't miss the last page because of round-off error") Signed-off-by: Gavin Shan Acked-by: Roman Gushchin Cc: [4.20+] Signed-off-by: Andrew Morton --- mm/vmscan.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) --- a/mm/vmscan.c~mm-vmscan-dont-round-up-scan-size-for-online-memory-cgroup +++ a/mm/vmscan.c @@ -2415,10 +2415,13 @@ out: /* * Scan types proportional to swappiness and * their relative recent reclaim efficiency. - * Make sure we don't miss the last page - * because of a round-off error. + * Make sure we don't miss the last page on + * the offlined memory cgroups because of a + * round-off error. */ - scan = DIV64_U64_ROUND_UP(scan * fraction[file], + scan = mem_cgroup_online(memcg) ? + div64_u64(scan * fraction[file], denominator) : + DIV64_U64_ROUND_UP(scan * fraction[file], denominator); break; case SCAN_FILE: _ Patches currently in -mm which might be from gshan@redhat.com are mm-vmscan-dont-round-up-scan-size-for-online-memory-cgroup.patch