Hi Ying,
> -----Original Message-----
> From: Huang, Ying <ying.huang@xxxxxxxxx>
> Sent: Wednesday, September 25, 2024 5:45 PM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx;
> hannes@xxxxxxxxxxx; yosryahmed@xxxxxxxxxx; nphamcs@xxxxxxxxx;
> chengming.zhou@xxxxxxxxx; usamaarif642@xxxxxxxxx;
> shakeel.butt@xxxxxxxxx; ryan.roberts@xxxxxxx; 21cnbao@xxxxxxxxx;
> akpm@xxxxxxxxxxxxxxxxxxxx; Zou, Nanhai <nanhai.zou@xxxxxxxxx>; Feghali,
> Wajdi K <wajdi.k.feghali@xxxxxxxxx>; Gopal, Vinodh
> <vinodh.gopal@xxxxxxxxx>
> Subject: Re: [PATCH v7 0/8] mm: ZSWAP swap-out of mTHP folios
>
> "Sridhar, Kanchana P" <kanchana.p.sridhar@xxxxxxxxx> writes:
>
> >> -----Original Message-----
> >> From: Huang, Ying <ying.huang@xxxxxxxxx>
> >> Sent: Tuesday, September 24, 2024 11:35 PM
> >> To: Sridhar, Kanchana P <kanchana.p.sridhar@xxxxxxxxx>
> >> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx;
> >> hannes@xxxxxxxxxxx; yosryahmed@xxxxxxxxxx; nphamcs@xxxxxxxxx;
> >> chengming.zhou@xxxxxxxxx; usamaarif642@xxxxxxxxx;
> >> shakeel.butt@xxxxxxxxx; ryan.roberts@xxxxxxx; 21cnbao@xxxxxxxxx;
> >> akpm@xxxxxxxxxxxxxxxxxxxx; Zou, Nanhai <nanhai.zou@xxxxxxxxx>;
> Feghali,
> >> Wajdi K <wajdi.k.feghali@xxxxxxxxx>; Gopal, Vinodh
> >> <vinodh.gopal@xxxxxxxxx>
> >> Subject: Re: [PATCH v7 0/8] mm: ZSWAP swap-out of mTHP folios
> >>
> >> Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx> writes:
> >>
> >> [snip]
> >>
> >> >
> >> > Case 1: Comparing zswap 4K vs. zswap mTHP
> >> > =========================================
> >> >
> >> > In this scenario, the "before" is CONFIG_THP_SWAP set to off, that
> results in
> >> > 64K/2M (m)THP to be split into 4K folios that get processed by zswap.
> >> >
> >> > The "after" is CONFIG_THP_SWAP set to on, and this patch-series, that
> >> results
> >> > in 64K/2M (m)THP to not be split, and processed by zswap.
> >> >
> >> > 64KB mTHP (cgroup memory.high set to 40G):
> >> > ==========================================
> >> >
> >> > -------------------------------------------------------------------------------
> >> > mm-unstable 9-23-2024 zswap-mTHP Change wrt
> >> > CONFIG_THP_SWAP=N CONFIG_THP_SWAP=Y
> Baseline
> >> > Baseline
> >> > -------------------------------------------------------------------------------
> >> > ZSWAP compressor zstd deflate- zstd deflate- zstd deflate-
> >> > iaa iaa iaa
> >> > -------------------------------------------------------------------------------
> >> > Throughput (KB/s) 143,323 125,485 153,550 129,609 7%
> 3%
> >> > elapsed time (sec) 24.97 25.42 23.90 25.19 4% 1%
> >> > sys time (sec) 822.72 750.96 757.70 731.13 8% 3%
> >> > memcg_high 132,743 169,825 148,075 192,744
> >> > memcg_swap_fail 639,067 841,553 2,204 2,215
> >> > pswpin 0 0 0 0
> >> > pswpout 0 0 0 0
> >> > zswpin 795 873 760 902
> >> > zswpout 10,011,266 13,195,137 10,010,017 13,193,554
> >> > thp_swpout 0 0 0 0
> >> > thp_swpout_ 0 0 0 0
> >> > fallback
> >> > 64kB-mthp_ 639,065 841,553 2,204 2,215
> >> > swpout_fallback
> >> > pgmajfault 2,861 2,924 3,054 3,259
> >> > ZSWPOUT-64kB n/a n/a 623,451 822,268
> >> > SWPOUT-64kB 0 0 0 0
> >> > -------------------------------------------------------------------------------
> >> >
> >>
> >> IIUC, the throughput is the sum of throughput of all usemem processes?
> >>
> >> One possible issue of usemem test case is the "imbalance" issue. That
> >> is, some usemem processes may swap-out/swap-in less, so the score is
> >> very high; while some other processes may swap-out/swap-in more, so the
> >> score is very low. Sometimes, the total score decreases, but the scores
> >> of usemem processes are more balanced, so that the performance should
> be
> >> considered better. And, in general, we should make usemem score
> >> balanced among processes via say longer test time. Can you check this
> >> in your test results?
> >
> > Actually, the throughput data listed in the cover-letter is the average of
> > all the usemem processes. Your observation about the "imbalance" issue is
> > right. Some processes see a higher throughput than others. I have noticed
> > that the throughputs progressively reduce as the individual processes exit
> > and print their stats.
> >
> > Listed below are the stats from two runs of usemem70: sleep 10 and sleep
> 30.
> > Both are run with a cgroup mem-limit of 40G. Data is with v7, 64K folios are
> > enabled, zswap uses zstd.
> >
> >
> > -----------------------------------------------
> > sleep 10 sleep 30
> > Throughput (KB/s) Throughput (KB/s)
> > -----------------------------------------------
> > 181,540 191,686
> > 179,651 191,459
> > 179,068 188,834
> > 177,244 187,568
> > 177,215 186,703
> > 176,565 185,584
> > 176,546 185,370
> > 176,470 185,021
> > 176,214 184,303
> > 176,128 184,040
> > 175,279 183,932
> > 174,745 180,831
> > 173,935 179,418
> > 161,546 168,014
> > 160,332 167,540
> > 160,122 167,364
> > 159,613 167,020
> > 159,546 166,590
> > 159,021 166,483
> > 158,845 166,418
> > 158,426 166,264
> > 158,396 166,066
> > 158,371 165,944
> > 158,298 165,866
> > 158,250 165,884
> > 158,057 165,533
> > 158,011 165,532
> > 157,899 165,457
> > 157,894 165,424
> > 157,839 165,410
> > 157,731 165,407
> > 157,629 165,273
> > 157,626 164,867
> > 157,581 164,636
> > 157,471 164,266
> > 157,430 164,225
> > 157,287 163,290
> > 156,289 153,597
> > 153,970 147,494
> > 148,244 147,102
> > 142,907 146,111
> > 142,811 145,789
> > 139,171 141,168
> > 136,314 140,714
> > 133,616 140,111
> > 132,881 139,636
> > 132,729 136,943
> > 132,680 136,844
> > 132,248 135,726
> > 132,027 135,384
> > 131,929 135,270
> > 131,766 134,748
> > 131,667 134,733
> > 131,576 134,582
> > 131,396 134,302
> > 131,351 134,160
> > 131,135 134,102
> > 130,885 134,097
> > 130,854 134,058
> > 130,767 134,006
> > 130,666 133,960
> > 130,647 133,894
> > 130,152 133,837
> > 130,006 133,747
> > 129,921 133,679
> > 129,856 133,666
> > 129,377 133,564
> > 128,366 133,331
> > 127,988 132,938
> > 126,903 132,746
> > -----------------------------------------------
> > sum 10,526,916 10,919,561
> > average 150,385 155,994
> > stddev 17,551 19,633
> > -----------------------------------------------
> > elapsed 24.40 43.66
> > time (sec)
> > sys time 806.25 766.05
> > (sec)
> > zswpout 10,008,713 10,008,407
> > 64K folio 623,463 623,629
> > swpout
> > -----------------------------------------------
>
> Although there are some imbalance, I don't find it's too much. So, I
> think the test result is reasonable. Please pay attention to the
> imbalance issue in the future tests.
Sure, will do so.
>
> > As we increase the time for which allocations are maintained,
> > there seems to be a slight improvement in throughput, but the
> > variance increases as well. The processes with lower throughput
> > could be the ones that handle the memcg being over limit by
> > doing reclaim, possibly before they can allocate.
> >
> > Interestingly, the longer test time does seem to reduce the amount
> > of reclaim (hence lower sys time), but more 64K large folios seem to
> > be reclaimed. Could this mean that with longer test time (sleep 30),
> > more cold memory residing in large folios is getting reclaimed, as
> > against memory just relinquished by the exiting processes?
>
> I don't think longer sleep time in test helps much to balance. Can you
> try with less process, and larger memory size per process? I guess that
> this will improve balance.
I tried this, and the data is listed below:
usemem options:
---------------
30 processes allocate 10G each
cgroup memory limit = 150G
sleep 10
525Gi SSD disk swap partition
64K large folios enabled
Throughput (KB/s) of each of the 30 processes:
---------------------------------------------------------------
mm-unstable zswap_store of large folios
9-25-2024 v7
zswap compressor: zstd zstd deflate-iaa
---------------------------------------------------------------
38,393 234,485 374,427
37,283 215,528 314,225
37,156 214,942 304,413
37,143 213,073 304,146
36,814 212,904 290,186
36,277 212,304 288,212
36,104 212,207 285,682
36,000 210,173 270,661
35,994 208,487 256,960
35,979 207,788 248,313
35,967 207,714 235,338
35,966 207,703 229,335
35,835 207,690 221,697
35,793 207,418 221,600
35,692 206,160 219,346
35,682 206,128 219,162
35,681 205,817 219,155
35,678 205,546 214,862
35,678 205,523 214,710
35,677 204,951 214,282
35,677 204,283 213,441
35,677 203,348 213,011
35,675 203,028 212,923
35,673 201,922 212,492
35,672 201,660 212,225
35,672 200,724 211,808
35,672 200,324 211,420
35,671 199,686 211,413
35,667 198,858 211,346
35,667 197,590 211,209
---------------------------------------------------------------
sum 1,081,515 6,217,964 7,268,000
average 36,051 207,265 242,267
stddev 655 7,010 42,234
elapsed time (sec) 343.70 107.40 84.34
sys time (sec) 269.30 2,520.13 1,696.20
memcg.high breaches 443,672 475,074 623,333
zswpout 22,605 48,931,249 54,777,100
pswpout 40,004,528 0 0
hugepages-64K zswpout 0 3,057,090 3,421,855
hugepages-64K swpout 2,500,283 0 0
---------------------------------------------------------------
As you can see, this is quite a memory-constrained scenario, where we
are giving a 50% of total memory required, as the memory limit for the
cgroup in which the 30 processes are run. This causes significantly more
reclaim activity than the setup I was using thus far (70 processes, 1G,
40G limit).
The variance or "imbalance" reduces somewhat for zstd, but not for IAA.
IAA shows really good throughput (17%) and elapsed time (21%) and
sys time (33%) improvement wrt zstd with zswap_store of large folios.
These are the memory-constrained scenarios in which IAA typically
does really well. IAA verify_compress is enabled, so this is an added
data integrity checks benefit we get with IAA.
I would like to get your and the maintainers' feedback on whether
I should switch to this "usemem30-10G" setup for v8?
Thanks,
Kanchana
>
> --
> Best Regards,
> Huang, Ying
