linux-kernel - Re: [lkp-robot] [mm] 7674270022: will-it-scale.per_process

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Date:   Thu, 10 Aug 2017 13:20:40 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     Ye Xiaolong <xiaolong.ye@...el.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Tony Luck <tony.luck@...el.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Jeff Dike <jdike@...toit.com>, linux-arch@...r.kernel.org,
        lkp@...org
Subject: Re: [lkp-robot] [mm]  7674270022:  will-it-scale.per_process_ops
 -19.3% regression

On Wed, Aug 09, 2017 at 09:14:50PM -0700, Nadav Amit wrote:

Hi Nadav,

< snip >

> >>>>> According to the description it is "testcase:brk increase/decrease of one
> >>>>> page”. According to the mode it spawns multiple processes, not threads.
> >>>>> 
> >>>>> Since a single page is unmapped each time, and the iTLB-loads increase
> >>>>> dramatically, I would suspect that for some reason a full TLB flush is
> >>>>> caused during do_munmap().
> >>>>> 
> >>>>> If I find some free time, I’ll try to profile the workload - but feel free
> >>>>> to beat me to it.
> >>>> 
> >>>> The root-cause appears to be that tlb_finish_mmu() does not call
> >>>> dec_tlb_flush_pending() - as it should. Any chance you can take care of it?
> >>> 
> >>> Oops, but with second looking, it seems it's not my fault. ;-)
> >>> https://marc.info/?l=linux-mm&m=150156699114088&w=2
> >>> 
> >>> Anyway, thanks for the pointing out.
> >>> xiaolong.ye, could you retest with this fix?
> >> 
> >> I've queued tests for 5 times and results show this patch (e8f682574e4 "mm:
> >> decrease tlb flush pending count in tlb_finish_mmu") does help recover the
> >> performance back.
> >> 
> >> 378005bdbac0a2ec  76742700225cad9df49f053993  e8f682574e45b6406dadfffeb4  
> >> ----------------  --------------------------  --------------------------  
> >>         %stddev      change         %stddev      change         %stddev
> >>             \          |                \          |                \  
> >>   3405093             -19%    2747088              -2%    3348752        will-it-scale.per_process_ops
> >>      1280 ±  3%        -2%       1257 ±  3%        -6%       1207        vmstat.system.cs
> >>      2702 ± 18%        11%       3002 ± 19%        17%       3156 ± 18%  numa-vmstat.node0.nr_mapped
> >>     10765 ± 18%        11%      11964 ± 19%        17%      12588 ± 18%  numa-meminfo.node0.Mapped
> >>      0.00 ± 47%       -40%       0.00 ± 45%       -84%       0.00 ± 42%  mpstat.cpu.soft%
> >> 
> >> Thanks,
> >> Xiaolong
> > 
> > Thanks for the testing!
> 
> Sorry again for screwing your patch, Minchan.

Never mind! It always happens. :)
In this chance, I really appreciates your insight/testing/cooperation!