On Wed, Jun 08, 2016 at 11:58:11AM +0300, Kirill A. Shutemov wrote:
> On Wed, Jun 08, 2016 at 04:41:37PM +0800, Huang, Ying wrote:
> > "Huang, Ying" <ying.hu...@intel.com> writes:
> >
> > > "Kirill A. Shutemov" <kirill.shute...@linux.intel.com> writes:
> > >
> > >> On Mon, Jun 06, 2016 at 10:27:24AM +0800, kernel test robot wrote:
> > >>>
> > >>> FYI, we noticed a -6.3% regression of unixbench.score due to commit:
> > >>>
> > >>> commit 5c0a85fad949212b3e059692deecdeed74ae7ec7 ("mm: make faultaround
> > >>> produce old ptes")
> > >>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> > >>> master
> > >>>
> > >>> in testcase: unixbench
> > >>> on test machine: lituya: 16 threads Haswell High-end Desktop (i7-5960X
> > >>> 3.0G) with 16G memory
> > >>> with following parameters:
> > >>> cpufreq_governor=performance/nr_task=1/test=shell8
> > >>>
> > >>>
> > >>> Details are as below:
> > >>> -------------------------------------------------------------------------------------------------->
> > >>>
> > >>>
> > >>> =========================================================================================
> > >>> compiler/cpufreq_governor/kconfig/nr_task/rootfs/tbox_group/test/testcase:
> > >>>
> > >>> gcc-4.9/performance/x86_64-rhel/1/debian-x86_64-2015-02-07.cgz/lituya/shell8/unixbench
> > >>>
> > >>> commit:
> > >>> 4b50bcc7eda4d3cc9e3f2a0aa60e590fedf728c5
> > >>> 5c0a85fad949212b3e059692deecdeed74ae7ec7
> > >>>
> > >>> 4b50bcc7eda4d3cc 5c0a85fad949212b3e059692de
> > >>> ---------------- --------------------------
> > >>> fail:runs %reproduction fail:runs
> > >>> | | |
> > >>> 3:4 -75% :4
> > >>> kmsg.DHCP/BOOTP:Reply_not_for_us,op[#]xid[#]
> > >>> %stddev %change %stddev
> > >>> \ | \
> > >>> 14321 . 0% -6.3% 13425 . 0% unixbench.score
> > >>> 1996897 . 0% -6.1% 1874635 . 0%
> > >>> unixbench.time.involuntary_context_switches
> > >>> 1.721e+08 . 0% -6.2% 1.613e+08 . 0%
> > >>> unixbench.time.minor_page_faults
> > >>> 758.65 . 0% -3.0% 735.86 . 0% unixbench.time.system_time
> > >>> 387.66 . 0% +5.4% 408.49 . 0% unixbench.time.user_time
> > >>> 5950278 . 0% -6.2% 5583456 . 0%
> > >>> unixbench.time.voluntary_context_switches
> > >>
> > >> That's weird.
> > >>
> > >> I don't understand why the change would reduce number or minor faults.
> > >> It should stay the same on x86-64. Rise of user_time is puzzling too.
> > >
> > > unixbench runs in fixed time mode. That is, the total time to run
> > > unixbench is fixed, but the work done varies. So the minor_page_faults
> > > change may reflect only the work done.
> > >
> > >> Hm. Is reproducible? Across reboot?
> > >
> >
> > And FYI, there is no swap setup for test, all root file system including
> > benchmark files are in tmpfs, so no real page reclaim will be
> > triggered. But it appears that active file cache reduced after the
> > commit.
> >
> > 111331 ± 1% -13.3% 96503 ± 0% meminfo.Active
> > 27603 ± 1% -43.9% 15486 ± 0% meminfo.Active(file)
> >
> > I think this is the expected behavior of the commit?
>
> Yes, it's expected.
>
> After the change faularound would produce old pte. It means there's more
> chance for these pages to be on inactive lru, unless somebody actually
> touch them and flip accessed bit.
Hmm, tmpfs pages should be in anonymous LRU list and VM shouldn't scan
anonymous LRU list on swapless system so I really wonder why active file
LRU is shrunk.
