Re: [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3% regression
From: Vlastimil Babka
Date: Tue Nov 27 2018 - 14:05:40 EST
On 11/27/18 6:08 PM, Linus Torvalds wrote:
> On Mon, Nov 26, 2018 at 10:24 PM kernel test robot
> <rong.a.chen@xxxxxxxxx> wrote:
>>
>> FYI, we noticed a -61.3% regression of vm-scalability.throughput due
>> to commit ac5b2c18911f ("mm: thp: relax __GFP_THISNODE for
>> MADV_HUGEPAGE mappings")
>
> Well, that's certainly noticeable and not good.
>
> Andrea, I suspect it might be causing fights with auto numa migration..
>
> Lots more system time, but also look at this:
>
>> 1122389 Â 9% +17.2% 1315380 Â 4% proc-vmstat.numa_hit
>> 214722 Â 5% +21.6% 261076 Â 3% proc-vmstat.numa_huge_pte_updates
>> 1108142 Â 9% +17.4% 1300857 Â 4% proc-vmstat.numa_local
>> 145368 Â 48% +63.1% 237050 Â 17% proc-vmstat.numa_miss
>> 159615 Â 44% +57.6% 251573 Â 16% proc-vmstat.numa_other
>> 185.50 Â 81% +8278.6% 15542 Â 40% proc-vmstat.numa_pages_migrated
>
> Should the commit be reverted? Or perhaps at least modified?
This part of the test's config is important:
thp_defrag: always
While the commit targets MADV_HUGEPAGE mappings (such as Andrea's
kvm-qemu usecase), with defrag=always, all mappings behave almost as a
MADV_HUGEPAGE mapping. That's no longer a default for some years now and
I think nobody recommends it. In the default configuration nothing
changes for non-madvise mappings.
Vlastimil
> Linus
>