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From: Yu Zhao <yuzhao@google.com>
Date: Mon, 18 Dec 2023 20:21:01 -0700
Message-ID: <CAOUHufZFkdDjCdQKBV5+W_bp_7x5VwrwkYbJeDdQ19S=m4Mc6A@mail.gmail.com>
Subject: Re: [PATCH mm-unstable v1 1/4] mm/mglru: fix underprotected page cache
To: Kairui Song <ryncsn@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, 
	linux-kernel@vger.kernel.org, Charan Teja Kalla <quic_charante@quicinc.com>, 
	Kalesh Singh <kaleshsingh@google.com>, stable@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Mon, Dec 18, 2023 at 11:05=E2=80=AFAM Kairui Song <ryncsn@gmail.com> wro=
te:
>
> Yu Zhao <yuzhao@google.com> =E4=BA=8E2023=E5=B9=B412=E6=9C=8815=E6=97=A5=
=E5=91=A8=E4=BA=94 12:56=E5=86=99=E9=81=93=EF=BC=9A
> >
> > On Thu, Dec 14, 2023 at 04:51:00PM -0700, Yu Zhao wrote:
> > > On Thu, Dec 14, 2023 at 11:38=E2=80=AFAM Kairui Song <ryncsn@gmail.co=
m> wrote:
> > > >
> > > > Yu Zhao <yuzhao@google.com> =E4=BA=8E2023=E5=B9=B412=E6=9C=8814=E6=
=97=A5=E5=91=A8=E5=9B=9B 11:09=E5=86=99=E9=81=93=EF=BC=9A
> > > > > On Wed, Dec 13, 2023 at 12:59:14AM -0700, Yu Zhao wrote:
> > > > > > On Tue, Dec 12, 2023 at 8:03=E2=80=AFPM Kairui Song <ryncsn@gma=
il.com> wrote:
> > > > > > >
> > > > > > > Kairui Song <ryncsn@gmail.com> =E4=BA=8E2023=E5=B9=B412=E6=9C=
=8812=E6=97=A5=E5=91=A8=E4=BA=8C 14:52=E5=86=99=E9=81=93=EF=BC=9A
> > > > > > > >
> > > > > > > > Yu Zhao <yuzhao@google.com> =E4=BA=8E2023=E5=B9=B412=E6=9C=
=8812=E6=97=A5=E5=91=A8=E4=BA=8C 06:07=E5=86=99=E9=81=93=EF=BC=9A
> > > > > > > > >
> > > > > > > > > On Fri, Dec 8, 2023 at 1:24=E2=80=AFAM Kairui Song <ryncs=
n@gmail.com> wrote:
> > > > > > > > > >
> > > > > > > > > > Yu Zhao <yuzhao@google.com> =E4=BA=8E2023=E5=B9=B412=E6=
=9C=888=E6=97=A5=E5=91=A8=E4=BA=94 14:14=E5=86=99=E9=81=93=EF=BC=9A
> > > > > > > > > > >
> > > > > > > > > > > Unmapped folios accessed through file descriptors can=
 be
> > > > > > > > > > > underprotected. Those folios are added to the oldest =
generation based
> > > > > > > > > > > on:
> > > > > > > > > > > 1. The fact that they are less costly to reclaim (no =
need to walk the
> > > > > > > > > > >    rmap and flush the TLB) and have less impact on pe=
rformance (don't
> > > > > > > > > > >    cause major PFs and can be non-blocking if needed =
again).
> > > > > > > > > > > 2. The observation that they are likely to be single-=
use. E.g., for
> > > > > > > > > > >    client use cases like Android, its apps parse conf=
iguration files
> > > > > > > > > > >    and store the data in heap (anon); for server use =
cases like MySQL,
> > > > > > > > > > >    it reads from InnoDB files and holds the cached da=
ta for tables in
> > > > > > > > > > >    buffer pools (anon).
> > > > > > > > > > >
> > > > > > > > > > > However, the oldest generation can be very short live=
d, and if so, it
> > > > > > > > > > > doesn't provide the PID controller with enough time t=
o respond to a
> > > > > > > > > > > surge of refaults. (Note that the PID controller uses=
 weighted
> > > > > > > > > > > refaults and those from evicted generations only take=
 a half of the
> > > > > > > > > > > whole weight.) In other words, for a short lived gene=
ration, the
> > > > > > > > > > > moving average smooths out the spike quickly.
> > > > > > > > > > >
> > > > > > > > > > > To fix the problem:
> > > > > > > > > > > 1. For folios that are already on LRU, if they can be=
 beyond the
> > > > > > > > > > >    tracking range of tiers, i.e., five accesses throu=
gh file
> > > > > > > > > > >    descriptors, move them to the second oldest genera=
tion to give them
> > > > > > > > > > >    more time to age. (Note that tiers are used by the=
 PID controller
> > > > > > > > > > >    to statistically determine whether folios accessed=
 multiple times
> > > > > > > > > > >    through file descriptors are worth protecting.)
> > > > > > > > > > > 2. When adding unmapped folios to LRU, adjust the pla=
cement of them so
> > > > > > > > > > >    that they are not too close to the tail. The effec=
t of this is
> > > > > > > > > > >    similar to the above.
> > > > > > > > > > >
> > > > > > > > > > > On Android, launching 55 apps sequentially:
> > > > > > > > > > >                            Before     After      Chan=
ge
> > > > > > > > > > >   workingset_refault_anon  25641024   25598972   0%
> > > > > > > > > > >   workingset_refault_file  115016834  106178438  -8%
> > > > > > > > > >
> > > > > > > > > > Hi Yu,
> > > > > > > > > >
> > > > > > > > > > Thanks you for your amazing works on MGLRU.
> > > > > > > > > >
> > > > > > > > > > I believe this is the similar issue I was trying to res=
olve previously:
> > > > > > > > > > https://lwn.net/Articles/945266/
> > > > > > > > > > The idea is to use refault distance to decide if the pa=
ge should be
> > > > > > > > > > place in oldest generation or some other gen, which per=
 my test,
> > > > > > > > > > worked very well, and we have been using refault distan=
ce for MGLRU in
> > > > > > > > > > multiple workloads.
> > > > > > > > > >
> > > > > > > > > > There are a few issues left in my previous RFC series, =
like anon pages
> > > > > > > > > > in MGLRU shouldn't be considered, I wanted to collect f=
eedback or test
> > > > > > > > > > cases, but unfortunately it seems didn't get too much a=
ttention
> > > > > > > > > > upstream.
> > > > > > > > > >
> > > > > > > > > > I think both this patch and my previous series are for =
solving the
> > > > > > > > > > file pages underpertected issue, and I did a quick test=
 using this
> > > > > > > > > > series, for mongodb test, refault distance seems still =
a better
> > > > > > > > > > solution (I'm not saying these two optimization are mut=
ually exclusive
> > > > > > > > > > though, just they do have some conflicts in implementat=
ion and solving
> > > > > > > > > > similar problem):
> > > > > > > > > >
> > > > > > > > > > Previous result:
> > > > > > > > > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > > > > > > > > > Execution Results after 905 seconds
> > > > > > > > > > -------------------------------------------------------=
-----------
> > > > > > > > > >                   Executed        Time (=C2=B5s)       =
Rate
> > > > > > > > > >   STOCK_LEVEL     2542            27121571486.2   0.09 =
txn/s
> > > > > > > > > > -------------------------------------------------------=
-----------
> > > > > > > > > >   TOTAL           2542            27121571486.2   0.09 =
txn/s
> > > > > > > > > >
> > > > > > > > > > This patch:
> > > > > > > > > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > > > > > > > > > Execution Results after 900 seconds
> > > > > > > > > > -------------------------------------------------------=
-----------
> > > > > > > > > >                   Executed        Time (=C2=B5s)       =
Rate
> > > > > > > > > >   STOCK_LEVEL     1594            27061522574.4   0.06 =
txn/s
> > > > > > > > > > -------------------------------------------------------=
-----------
> > > > > > > > > >   TOTAL           1594            27061522574.4   0.06 =
txn/s
> > > > > > > > > >
> > > > > > > > > > Unpatched version is always around ~500.
> > > > > > > > >
> > > > > > > > > Thanks for the test results!
> > > > > > > > >
> > > > > > > > > > I think there are a few points here:
> > > > > > > > > > - Refault distance make use of page shadow so it can be=
tter
> > > > > > > > > > distinguish evicted pages of different access pattern (=
re-access
> > > > > > > > > > distance).
> > > > > > > > > > - Throttled refault distance can help hold part of work=
ingset when
> > > > > > > > > > memory is too small to hold the whole workingset.
> > > > > > > > > >
> > > > > > > > > > So maybe part of this patch and the bits of previous se=
ries can be
> > > > > > > > > > combined to work better on this issue, how do you think=
?
> > > > > > > > >
> > > > > > > > > I'll try to find some time this week to look at your RFC.=
 It'd be a
> > > > > > >
> > > > > > > Hi Yu,
> > > > > > >
> > > > > > > I'm working on V4 of the RFC now, which just update some comm=
ents, and
> > > > > > > skip anon page re-activation in refault path for mglru which =
was not
> > > > > > > very helpful, only some tiny adjustment.
> > > > > > > And I found it easier to test with fio, using following test =
script:
> > > > > > >
> > > > > > > #!/bin/bash
> > > > > > > swapoff -a
> > > > > > >
> > > > > > > modprobe brd rd_nr=3D1 rd_size=3D16777216
> > > > > > > mkfs.ext4 /dev/ram0
> > > > > > > mount /dev/ram0 /mnt
> > > > > > >
> > > > > > > mkdir -p /sys/fs/cgroup/benchmark
> > > > > > > cd /sys/fs/cgroup/benchmark
> > > > > > >
> > > > > > > echo 4G > memory.max
> > > > > > > echo $$ > cgroup.procs
> > > > > > > echo 3 > /proc/sys/vm/drop_caches
> > > > > > >
> > > > > > > fio -name=3Dmglru --numjobs=3D12 --directory=3D/mnt --size=3D=
1024m \
> > > > > > >           --buffered=3D1 --ioengine=3Dio_uring --iodepth=3D12=
8 \
> > > > > > >           --iodepth_batch_submit=3D32 --iodepth_batch_complet=
e=3D32 \
> > > > > > >           --rw=3Drandread --random_distribution=3Dzipf:0.5 --=
norandommap \
> > > > > > >           --time_based --ramp_time=3D5m --runtime=3D5m --grou=
p_reporting
> > > > > > >
> > > > > > > zipf:0.5 is used here to simulate a cached read with slight b=
ias
> > > > > > > towards certain pages.
> > > > > > > Unpatched 6.7-rc4:
> > > > > > > Run status group 0 (all jobs):
> > > > > > >    READ: bw=3D6548MiB/s (6866MB/s), 6548MiB/s-6548MiB/s
> > > > > > > (6866MB/s-6866MB/s), io=3D1918GiB (2060GB), run=3D300001-3000=
01msec
> > > > > > >
> > > > > > > Patched with RFC v4:
> > > > > > > Run status group 0 (all jobs):
> > > > > > >    READ: bw=3D7270MiB/s (7623MB/s), 7270MiB/s-7270MiB/s
> > > > > > > (7623MB/s-7623MB/s), io=3D2130GiB (2287GB), run=3D300001-3000=
01msec
> > > > > > >
> > > > > > > Patched with this series:
> > > > > > > Run status group 0 (all jobs):
> > > > > > >    READ: bw=3D7098MiB/s (7442MB/s), 7098MiB/s-7098MiB/s
> > > > > > > (7442MB/s-7442MB/s), io=3D2079GiB (2233GB), run=3D300002-3000=
02msec
> > > > > > >
> > > > > > > MGLRU off:
> > > > > > > Run status group 0 (all jobs):
> > > > > > >    READ: bw=3D6525MiB/s (6842MB/s), 6525MiB/s-6525MiB/s
> > > > > > > (6842MB/s-6842MB/s), io=3D1912GiB (2052GB), run=3D300002-3000=
02msec
> > > > > > >
> > > > > > > - If I change zipf:0.5 to random:
> > > > > > > Unpatched 6.7-rc4:
> > > > > > > Patched with this series:
> > > > > > > Run status group 0 (all jobs):
> > > > > > >    READ: bw=3D5975MiB/s (6265MB/s), 5975MiB/s-5975MiB/s
> > > > > > > (6265MB/s-6265MB/s), io=3D1750GiB (1879GB), run=3D300002-3000=
02msec
> > > > > > >
> > > > > > > Patched with RFC v4:
> > > > > > > Run status group 0 (all jobs):
> > > > > > >    READ: bw=3D5987MiB/s (6278MB/s), 5987MiB/s-5987MiB/s
> > > > > > > (6278MB/s-6278MB/s), io=3D1754GiB (1883GB), run=3D300001-3000=
01msec
> > > > > > >
> > > > > > > Patched with this series:
> > > > > > > Run status group 0 (all jobs):
> > > > > > >    READ: bw=3D5839MiB/s (6123MB/s), 5839MiB/s-5839MiB/s
> > > > > > > (6123MB/s-6123MB/s), io=3D1711GiB (1837GB), run=3D300001-3000=
01msec
> > > > > > >
> > > > > > > MGLRU off:
> > > > > > > Run status group 0 (all jobs):
> > > > > > >    READ: bw=3D5689MiB/s (5965MB/s), 5689MiB/s-5689MiB/s
> > > > > > > (5965MB/s-5965MB/s), io=3D1667GiB (1790GB), run=3D300003-3000=
03msec
> > > > > > >
> > > > > > > fio uses ramdisk so LRU accuracy will have smaller impact. Th=
e Mongodb
> > > > > > > test I provided before uses a SATA SSD so it will have a much=
 higher
> > > > > > > impact. I'll provides a script to setup the test case and run=
 it, it's
> > > > > > > more complex to setup than fio since involving setting up mul=
tiple
> > > > > > > replicas and auth and hundreds of GB of test fixtures, I'm cu=
rrently
> > > > > > > occupied by some other tasks but will try best to send them o=
ut as
> > > > > > > soon as possible.
> > > > > >
> > > > > > Thanks! Apparently your RFC did show better IOPS with both acce=
ss
> > > > > > patterns, which was a surprise to me because it had higher refa=
ults
> > > > > > and usually higher refautls result in worse performance.
> >
> > And thanks for providing the refaults I requested for -- your data
> > below confirms what I mentioned above:
> >
> > For fio:
> >                            Your RFC   This series   Change
> >   workingset_refault_file  628192729  596790506     -5%
> >   IOPS                     1862k      1830k         -2%
> >
> > For MongoDB:
> >                            Your RFC   This series   Change
> >   workingset_refault_anon  10512      35277         +30%
> >   workingset_refault_file  22751782   20335355      -11%
> >   total                    22762294   20370632      -11%
> >   TPS                      0.09       0.06          -33%
> >
> > For MongoDB, this series should be a big win (but apparently it's not),
> > especially when using zram, since an anon refault should be a lot
> > cheaper than a file refault.
> >
> > So, I'm baffled...
> >
> > One important detail I forgot to mention: based on your data from
> > lru_gen_full, I think there is another difference between our Kconfigs:
> >
> >                   Your Kconfig  My Kconfig  Max possible
> >   LRU_REFS_WIDTH  1             2           2
>
> Hi Yu,
>
> Thanks for the info, my fault, I forgot to update my config as I was
> testing some other features.
> Buf after I changed LRU_REFS_WIDTH to 2 by disabling IDLE_PAGE, thing
> got much worse for MongoDB test:
>
> With LRU_REFS_WIDTH =3D=3D 2:
>
> This patch:
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> Execution Results after 919 seconds
> ------------------------------------------------------------------
>                   Executed        Time (=C2=B5s)       Rate
>   STOCK_LEVEL     488             27598136201.9   0.02 txn/s
> ------------------------------------------------------------------
>   TOTAL           488             27598136201.9   0.02 txn/s
>
> memcg    86 /system.slice/docker-1c3a90be9f0a072f5719332419550cd0e1455f2c=
d5863bc2780ca4d3f913ece5.scope
>  node     0
>           1     948187          0x          0x
>                      0          0           0           0           0
>          0           0=C2=B7
>                      1          0           0           0           0
>          0           0=C2=B7
>                      2          0           0           0           0
>          0           0=C2=B7
>                      3          0           0           0           0
>          0           0=C2=B7
>                                 0           0           0           0
>          0           0=C2=B7
>           2     948187          0     6051788=C2=B7
>                      0          0r          0e          0p      11916r
>      66442e          0p
>                      1          0r          0e          0p        903r
>      16888e          0p
>                      2          0r          0e          0p        459r
>       9764e          0p
>                      3          0r          0e          0p          0r
>          0e       2874p
>                                 0           0           0           0
>          0           0=C2=B7
>           3     948187    1353160        6351=C2=B7
>                      0          0           0           0           0
>          0           0=C2=B7
>                      1          0           0           0           0
>          0           0=C2=B7
>                      2          0           0           0           0
>          0           0=C2=B7
>                      3          0           0           0           0
>          0           0=C2=B7
>                                 0           0           0           0
>          0           0=C2=B7
>           4      73045      23573          12=C2=B7
>                      0          0R          0T          0     3498607R
>    4868605T          0=C2=B7
>                      1          0R          0T          0     3012246R
>    3270261T          0=C2=B7
>                      2          0R          0T          0     2498608R
>    2839104T          0=C2=B7
>                      3          0R          0T          0           0R
>    1983947T          0=C2=B7
>                           1486579L          0O    1380614Y       2945N
>       2945F       2734A
>
> workingset_refault_anon 0
> workingset_refault_file 18130598
>
>               total        used        free      shared  buff/cache   ava=
ilable
> Mem:          31978        6705         312          20       24960      =
 24786
> Swap:         31977           4       31973
>
> RFC:
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> Execution Results after 908 seconds
> ------------------------------------------------------------------
>                   Executed        Time (=C2=B5s)       Rate
>   STOCK_LEVEL     2252            27159962888.2   0.08 txn/s
> ------------------------------------------------------------------
>   TOTAL           2252            27159962888.2   0.08 txn/s
>
> workingset_refault_anon 22585
> workingset_refault_file 22715256
>
> memcg    66 /system.slice/docker-0989446ff78106e32d3f400a0cf371c9a703281b=
ded86d6d6bb1af706ebb25da.scope
>  node     0
>          22     563007       2274     1198225=C2=B7
>                      0          0r          1e          0p          0r
>     697076e          0p
>                      1          0r          0e          0p          0r
>          0e     325661p
>                      2          0r          0e          0p          0r
>          0e     888728p
>                      3          0r          0e          0p          0r
>          0e    3602238p
>                                 0           0           0           0
>          0           0=C2=B7
>          23     532222       7525     4948747=C2=B7
>                      0          0           0           0           0
>          0           0=C2=B7
>                      1          0           0           0           0
>          0           0=C2=B7
>                      2          0           0           0           0
>          0           0=C2=B7
>                      3          0           0           0           0
>          0           0=C2=B7
>                                 0           0           0           0
>          0           0=C2=B7
>          24     500367    1214667        3292=C2=B7
>                      0          0           0           0           0
>          0           0=C2=B7
>                      1          0           0           0           0
>          0           0=C2=B7
>                      2          0           0           0           0
>          0           0=C2=B7
>                      3          0           0           0           0
>          0           0=C2=B7
>                                 0           0           0           0
>          0           0=C2=B7
>          25     469692      40797         466=C2=B7
>                      0          0R        271T          0           0R
>    1162165T          0=C2=B7
>                      1          0R          0T          0      774028R
>    1205332T          0=C2=B7
>                      2          0R          0T          0           0R
>     932484T          0=C2=B7
>                      3          0R          1T          0           0R
>    4252158T          0=C2=B7
>                          25178380L     156515O   23953602Y      59234N
>      49391F      48664A
>
>               total        used        free      shared  buff/cache   ava=
ilable
> Mem:          31978        6968         338           5       24671      =
 24555
> Swap:         31977        1533       30444
>
> Using same mongodb config (a 3 replica cluster using the same config):
> {
>     "net": {
>         "bindIpAll": true,
>         "ipv6": false,
>         "maxIncomingConnections": 10000,
>     },
>     "setParameter": {
>         "disabledSecureAllocatorDomains": "*"
>     },
>     "replication": {
>         "oplogSizeMB": 10480,
>         "replSetName": "issa-tpcc_0"
>     },
>     "security": {
>         "keyFile": "/data/db/keyfile"
>     },
>     "storage": {
>         "dbPath": "/data/db/",
>         "syncPeriodSecs": 60,
>         "directoryPerDB": true,
>         "wiredTiger": {
>             "engineConfig": {
>                 "cacheSizeGB": 5
>             }
>         }
>     },
>     "systemLog": {
>         "destination": "file",
>         "logAppend": true,
>         "logRotate": "rename",
>         "path": "/data/db/mongod.log",
>         "verbosity": 0
>     }
> }
>
> The test environment have 32g memory and 16 core.
>
> Per my analyze, the access pattern for the mongodb test is that page
> will be re-access long after it's evicted so PID controller won't
> protect higher tier. That RFC will make use of the long existing
> shadow to do feedback to PID/Gen so the result will be much better.
> Still need more adjusting though, will try to do a rebase on top of
> mm-unstable which includes your patch.
>
> I've no idea why the workingset_refault_* is higher in the better
> case, this a clearly an IO bound workload, Memory and IO is busy while
> CPU is not full...
>
> I've uploaded my local reproducer here:
> https://github.com/ryncsn/emm-test-project/tree/master/mongo-cluster
> https://github.com/ryncsn/py-tpcc

Thanks for the repos -- I'm trying them right now. Which MongoDB
version did you use? setup.sh didn't seem to install it.

Also do you have a QEMU image? It'd be a lot easier for me to
duplicate the exact environment by looking into it.