linux-kernel - Re: [PATCH v7 0/8] mm: ZSWAP swap-out of mTHP folios

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Message-ID: <87v7yks0kd.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date: Wed, 25 Sep 2024 14:35:14 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>
Cc: <linux-kernel@...r.kernel.org>,  <linux-mm@...ck.org>,
  <hannes@...xchg.org>,  <yosryahmed@...gle.com>,  <nphamcs@...il.com>,
  <chengming.zhou@...ux.dev>,  <usamaarif642@...il.com>,
  <shakeel.butt@...ux.dev>,  <ryan.roberts@....com>,  <21cnbao@...il.com>,
  <akpm@...ux-foundation.org>,  <nanhai.zou@...el.com>,
  <wajdi.k.feghali@...el.com>,  <vinodh.gopal@...el.com>
Subject: Re: [PATCH v7 0/8] mm: ZSWAP swap-out of mTHP folios

Kanchana P Sridhar <kanchana.p.sridhar@...el.com> 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?

[snip]

--
Best Regards,
Huang, Ying