Re: [PATCH 4/4] mm: numa: Slow PTE scan rate if migration failures occur

From: Mel Gorman
Date: Tue Mar 10 2015 - 09:08:17 EST

On Mon, Mar 09, 2015 at 09:02:19PM +0000, Mel Gorman wrote:
> On Sun, Mar 08, 2015 at 08:40:25PM +0000, Mel Gorman wrote:
> > > Because if the answer is 'yes', then we can safely say: 'we regressed
> > > performance because correctness [not dropping dirty bits] comes before
> > > performance'.
> > >
> > > If the answer is 'no', then we still have a mystery (and a regression)
> > > to track down.
> > >
> > > As a second hack (not to be applied), could we change:
> > >
> > > #define _PAGE_BIT_PROTNONE _PAGE_BIT_GLOBAL
> > >
> > > to:
> > >
> > > #define _PAGE_BIT_PROTNONE (_PAGE_BIT_GLOBAL+1)
> > >
> >
> > In itself, that's not enough. The SWP_OFFSET_SHIFT would also need updating
> > as a partial revert of 21d9ee3eda7792c45880b2f11bff8e95c9a061fb but it
> > can be done.
> >
>
> More importantily, _PAGE_BIT_GLOBAL+1 == the special PTE bit so just
> updating the value should crash. For the purposes of testing the idea, I
> thought the straight-forward option was to break soft dirty page tracking
> and steal their bit for testing (patch below). Took most of the day to
> get access to the test machine so tests are not long running and only
> the autonuma one has completed;
>

And the xfsrepair workload also does not show any benefit from using a
different bit either

3.19.0 4.0.0-rc1 4.0.0-rc1 4.0.0-rc1
vanilla vanilla slowscan-v2r7 protnone-v3r17
Min real-fsmark 1164.44 ( 0.00%) 1157.41 ( 0.60%) 1150.38 ( 1.21%) 1173.22 ( -0.75%)
Min syst-fsmark 4016.12 ( 0.00%) 3998.06 ( 0.45%) 3988.42 ( 0.69%) 4037.90 ( -0.54%)
Min real-xfsrepair 442.64 ( 0.00%) 497.64 (-12.43%) 456.87 ( -3.21%) 489.60 (-10.61%)
Min syst-xfsrepair 194.97 ( 0.00%) 500.61 (-156.76%) 263.41 (-35.10%) 544.56 (-179.30%)
Amean real-fsmark 1166.28 ( 0.00%) 1166.63 ( -0.03%) 1155.97 ( 0.88%) 1183.19 ( -1.45%)
Amean syst-fsmark 4025.87 ( 0.00%) 4020.94 ( 0.12%) 4004.19 ( 0.54%) 4061.64 ( -0.89%)
Amean real-xfsrepair 447.66 ( 0.00%) 507.85 (-13.45%) 459.58 ( -2.66%) 498.71 (-11.40%)
Amean syst-xfsrepair 202.93 ( 0.00%) 519.88 (-156.19%) 281.63 (-38.78%) 569.21 (-180.50%)
Stddev real-fsmark 1.44 ( 0.00%) 6.55 (-354.10%) 3.97 (-175.65%) 9.20 (-537.90%)
Stddev syst-fsmark 9.76 ( 0.00%) 16.22 (-66.27%) 15.09 (-54.69%) 17.47 (-79.13%)
Stddev real-xfsrepair 5.57 ( 0.00%) 11.17 (-100.68%) 3.41 ( 38.66%) 6.77 (-21.63%)
Stddev syst-xfsrepair 5.69 ( 0.00%) 13.98 (-145.78%) 19.94 (-250.49%) 20.03 (-252.05%)
CoeffVar real-fsmark 0.12 ( 0.00%) 0.56 (-353.96%) 0.34 (-178.11%) 0.78 (-528.79%)
CoeffVar syst-fsmark 0.24 ( 0.00%) 0.40 (-66.48%) 0.38 (-55.53%) 0.43 (-77.55%)
CoeffVar real-xfsrepair 1.24 ( 0.00%) 2.20 (-76.89%) 0.74 ( 40.25%) 1.36 ( -9.17%)
CoeffVar syst-xfsrepair 2.80 ( 0.00%) 2.69 ( 4.06%) 7.08 (-152.54%) 3.52 (-25.51%)
Max real-fsmark 1167.96 ( 0.00%) 1171.98 ( -0.34%) 1159.25 ( 0.75%) 1195.41 ( -2.35%)
Max syst-fsmark 4039.20 ( 0.00%) 4033.84 ( 0.13%) 4024.53 ( 0.36%) 4079.45 ( -1.00%)
Max real-xfsrepair 455.42 ( 0.00%) 523.40 (-14.93%) 464.40 ( -1.97%) 505.82 (-11.07%)
Max syst-xfsrepair 207.94 ( 0.00%) 533.37 (-156.50%) 309.38 (-48.78%) 593.62 (-185.48%)

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