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BL1PR12MB5223.namprd12.prod.outlook.com (2603:10b6:208:315::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6411.21; Fri, 19 May 2023 07:56:55 +0000 Received: from IA1PR12MB6434.namprd12.prod.outlook.com ([fe80::e58a:85b5:25a4:8cd2]) by IA1PR12MB6434.namprd12.prod.outlook.com ([fe80::e58a:85b5:25a4:8cd2%6]) with mapi id 15.20.6387.033; Fri, 19 May 2023 07:56:55 +0000 Message-ID: <226b9290-deea-53f5-54b3-42ee52c67e1d@amd.com> Date: Fri, 19 May 2023 13:26:43 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [RFC PATCH V2 1/1] sched/numa: Fix disjoint set vma scan regression To: Raghavendra K T , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Ingo Molnar , Peter Zijlstra , Mel Gorman , Andrew Morton , David Hildenbrand , rppt@kernel.org, Juri Lelli , Vincent Guittot , Aithal Srikanth , kernel test robot References: Content-Language: en-US From: Bharata B Rao 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 tyCm+HIE 5o4bMCvYL+nbxzmfXnqUD9tUAwDUYTGH/tJILfd4SduxvJXcA85J6azCEMonExm6Tn6DGJY5wP6Gt40d0sOgIBhf82zFTgkHdU2D96J6jw6wNCFzSoKFSwSU6MAczBdJoxsfmvLCOHR/MuK/n+jeKK8AdA/QVarKXwV1rRGzSHTBagTLb13OLPRtyhYpyl56Cm4dLIEpFAk8buJMeKVasFC7LJ6oCXEu5hRGTrexYPYVJWE/JfWyzJk7LMZ39ewegkx4Ymw1016Q1tiy/0swqUDVk1c3TEL27B8XJ3AHCCSAqoT5poFC865cYJg== 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 16-May-23 2:49 PM, Raghavendra K T wrote: > With the numa scan enhancements [1], only the threads which had previously > accessed vma are allowed to scan. > > While this had improved significant system time overhead, there were corner > cases, which genuinely need some relaxation. For e.g., > > 1) Concern raised by PeterZ, where if there are N partition sets of vmas > belonging to tasks, then unfairness in allowing these threads to scan could > potentially amplify the side effect of some of the vmas being left > unscanned. > > 2) Below reports of LKP numa01 benchmark regression. > > Currently this was handled by allowing first two scanning unconditional > as indicated by mm->numa_scan_seq. This is imprecise since for some > benchmark vma scanning might itself start at numa_scan_seq > 2. > > Solution: > Allow unconditional scanning of vmas of tasks depending on vma size. This > is achieved by maintaining a per vma scan counter, where > > f(allowed_to_scan) = f(scan_counter < vma_size / scan_size) > > Fixes: fc137c0ddab2 ("sched/numa: enhance vma scanning logic") > regression. > > Result: > numa01_THREAD_ALLOC result on 6.4.0-rc1 (that has w/ numascan enhancement) > base-numascan base base+fix > real 1m3.025s 1m24.163s 1m3.551s > user 213m44.232s 251m3.638s 219m55.662s > sys 6m26.598s 0m13.056s 2m35.767s > > numa_hit 5478165 4395752 4907431 > numa_local 5478103 4395366 4907044 > numa_other 62 386 387 > numa_pte_updates 1989274 11606 1265014 > numa_hint_faults 1756059 515 1135804 > numa_hint_faults_local 971500 486 558076 > numa_pages_migrated 784211 29 577728 > > Summary: Regression in base is recovered by allowing scanning as required. > > [1] https://lore.kernel.org/lkml/cover.1677672277.git.raghavendra.kt@amd.com/T/#t > > Reported-by: Aithal Srikanth > Reported-by: kernel test robot > Closes: https://lore.kernel.org/lkml/db995c11-08ba-9abf-812f-01407f70a5d4@amd.com/T/ > Signed-off-by: Raghavendra K T > --- > include/linux/mm_types.h | 1 + > kernel/sched/fair.c | 41 ++++++++++++++++++++++++++++++++-------- > 2 files changed, 34 insertions(+), 8 deletions(-) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 306a3d1a0fa6..992e460a713e 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -479,6 +479,7 @@ struct vma_numab_state { > unsigned long next_scan; > unsigned long next_pid_reset; > unsigned long access_pids[2]; > + unsigned int scan_counter; > }; > > /* > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 373ff5f55884..2c3e17e7fc2f 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2931,20 +2931,34 @@ static void reset_ptenuma_scan(struct task_struct *p) > static bool vma_is_accessed(struct vm_area_struct *vma) > { > unsigned long pids; > + unsigned int vma_size; > + unsigned int scan_threshold; > + unsigned int scan_size; > + > + pids = vma->numab_state->access_pids[0] | vma->numab_state->access_pids[1]; > + > + if (test_bit(hash_32(current->pid, ilog2(BITS_PER_LONG)), &pids)) > + return true; > + > + scan_size = READ_ONCE(sysctl_numa_balancing_scan_size); > + /* vma size in MB */ > + vma_size = (vma->vm_end - vma->vm_start) >> 20; > + > + /* Total scans needed to cover VMA */ > + scan_threshold = (vma_size / scan_size); > + > /* > - * Allow unconditional access first two times, so that all the (pages) > - * of VMAs get prot_none fault introduced irrespective of accesses. > + * Allow the scanning of half of disjoint set's VMA to induce > + * prot_none fault irrespective of accesses. > * This is also done to avoid any side effect of task scanning > * amplifying the unfairness of disjoint set of VMAs' access. > */ > - if (READ_ONCE(current->mm->numa_scan_seq) < 2) > - return true; > - > - pids = vma->numab_state->access_pids[0] | vma->numab_state->access_pids[1]; > - return test_bit(hash_32(current->pid, ilog2(BITS_PER_LONG)), &pids); > + scan_threshold = 1 + (scan_threshold >> 1); > + return (READ_ONCE(vma->numab_state->scan_counter) <= scan_threshold); > } > > -#define VMA_PID_RESET_PERIOD (4 * sysctl_numa_balancing_scan_delay) > +#define VMA_PID_RESET_PERIOD (4 * sysctl_numa_balancing_scan_delay) > +#define DISJOINT_VMA_SCAN_RENEW_THRESH 16 > > /* > * The expensive part of numa migration is done from task_work context. > @@ -3058,6 +3072,8 @@ static void task_numa_work(struct callback_head *work) > /* Reset happens after 4 times scan delay of scan start */ > vma->numab_state->next_pid_reset = vma->numab_state->next_scan + > msecs_to_jiffies(VMA_PID_RESET_PERIOD); > + > + WRITE_ONCE(vma->numab_state->scan_counter, 0); > } > > /* > @@ -3068,6 +3084,13 @@ static void task_numa_work(struct callback_head *work) > vma->numab_state->next_scan)) > continue; > > + /* > + * For long running tasks, renew the disjoint vma scanning > + * periodically. > + */ > + if (mm->numa_scan_seq && !(mm->numa_scan_seq % DISJOINT_VMA_SCAN_RENEW_THRESH)) Don't you need a READ_ONCE() accessor for mm->numa_scan_seq? Regards, Bharata.