Re: [linus:master] [mm] f822a9a81a: stress-ng.bigheap.realloc_calls_per_sec 37.3% regression

[Dev Jain <dev.jain@arm.com>]

On 07/08/25 1:57 pm, Lorenzo Stoakes wrote:
> On Thu, Aug 07, 2025 at 04:17:09PM +0800, kernel test robot wrote:
>>
>> Hello,
>>
>> kernel test robot noticed a 37.3% regression of stress-ng.bigheap.realloc_calls_per_sec on:
>>
> Dev - could you please investigate and provide a fix for this as a
> priority? As these numbers are quite scary (unless they're somehow super
> synthetic or not meaningful or something).

Yup I'll start looking.

>
>> commit: f822a9a81a31311d67f260aea96005540b18ab07 ("mm: optimize mremap() by PTE batching")
>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>>
>> [still regression on      linus/master 186f3edfdd41f2ae87fc40a9ccba52a3bf930994]
>> [still regression on linux-next/master b9ddaa95fd283bce7041550ddbbe7e764c477110]
>>
>> testcase: stress-ng
>> config: x86_64-rhel-9.4
>> compiler: gcc-12
>> test machine: 192 threads 2 sockets Intel(R) Xeon(R) Platinum 8468V  CPU @ 2.4GHz (Sapphire Rapids) with 384G memory
>> parameters:
>>
>> 	nr_threads: 100%
>> 	testtime: 60s
>> 	test: bigheap
>> 	cpufreq_governor: performance
>>
>>
>>
>>
>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>> the same patch/commit), kindly add following tags
>> | Reported-by: kernel test robot <oliver.sang@intel.com>
>> | Closes: https://lore.kernel.org/oe-lkp/202508071609.4e743d7c-lkp@intel.com
>>
>>
>> Details are as below:
>> -------------------------------------------------------------------------------------------------->
>>
>>
>> The kernel config and materials to reproduce are available at:
>> https://download.01.org/0day-ci/archive/20250807/202508071609.4e743d7c-lkp@intel.com
>>
>> =========================================================================================
>> compiler/cpufreq_governor/kconfig/nr_threads/rootfs/tbox_group/test/testcase/testtime:
>>    gcc-12/performance/x86_64-rhel-9.4/100%/debian-12-x86_64-20240206.cgz/igk-spr-2sp1/bigheap/stress-ng/60s
>>
>> commit:
>>    94dab12d86 ("mm: call pointers to ptes as ptep")
>>    f822a9a81a ("mm: optimize mremap() by PTE batching")
>>
>> 94dab12d86cf77ff f822a9a81a31311d67f260aea96
>> ---------------- ---------------------------
>>           %stddev     %change         %stddev
>>               \          |                \
>>       13777 ± 37%     +45.0%      19979 ± 27%  numa-vmstat.node1.nr_slab_reclaimable
>>      367205            +2.3%     375703        vmstat.system.in
>>       55106 ± 37%     +45.1%      79971 ± 27%  numa-meminfo.node1.KReclaimable
>>       55106 ± 37%     +45.1%      79971 ± 27%  numa-meminfo.node1.SReclaimable
>>      559381           -37.3%     350757        stress-ng.bigheap.realloc_calls_per_sec
>>       11468            +1.2%      11603        stress-ng.time.system_time
>>      296.25            +4.5%     309.70        stress-ng.time.user_time
>>        0.81 ±187%    -100.0%       0.00        perf-sched.sch_delay.avg.ms.__cond_resched.zap_pte_range.zap_pmd_range.isra.0
>>        9.36 ±165%    -100.0%       0.00        perf-sched.sch_delay.max.ms.__cond_resched.zap_pte_range.zap_pmd_range.isra.0
>>        0.81 ±187%    -100.0%       0.00        perf-sched.wait_time.avg.ms.__cond_resched.zap_pte_range.zap_pmd_range.isra.0
>>        9.36 ±165%    -100.0%       0.00        perf-sched.wait_time.max.ms.__cond_resched.zap_pte_range.zap_pmd_range.isra.0
>>        5.50 ± 17%    +390.9%      27.00 ± 56%  perf-c2c.DRAM.local
>>      388.50 ± 10%    +114.7%     834.17 ± 33%  perf-c2c.DRAM.remote
>>        1214 ± 13%    +107.3%       2517 ± 31%  perf-c2c.HITM.local
>>      135.00 ± 19%    +130.9%     311.67 ± 32%  perf-c2c.HITM.remote
>>        1349 ± 13%    +109.6%       2829 ± 31%  perf-c2c.HITM.total
> Yeah this also looks pretty consistent too...
>
> Yikes.