linux-kernel - Re: [PATCHv4 14/17] zsmalloc: make zspage lock preemptible

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Message-ID: <Z64O3w2p1NrXoicl@google.com>
Date: Thu, 13 Feb 2025 15:25:19 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Kairui Song <ryncsn@...il.com>
Subject: Re: [PATCHv4 14/17] zsmalloc: make zspage lock preemptible

On Thu, Feb 13, 2025 at 05:22:20PM +0900, Sergey Senozhatsky wrote:
> On (25/02/13 16:21), Sergey Senozhatsky wrote:
> > BASE
> > ====
> > 
> > 1363.64user 157.08system 1:30.89elapsed 1673%CPU (0avgtext+0avgdata 825692maxresident)k
> > 
> > lock stats
> > 
> >                               class name    con-bounces    contentions   waittime-min   waittime-max waittime-total   waittime-avg    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total   holdtime-avg
> >                    &pool->migrate_lock-R:             0              0           0.00           0.00           0.00           0.00          10001         702081           0.14         104.74      125571.64           0.18
> >                             &class->lock:             1              1           0.25           0.25           0.25           0.25           6320         840542           0.06         809.72      191214.87           0.23
> >                          &zspage->lock-R:             0              0           0.00           0.00           0.00           0.00           6452         664129           0.12         660.24      201888.61           0.30
> >                 &zram->table[index].lock:             0              0           0.00           0.00           0.00           0.00        1716362        3096466           0.07         811.10      365551.24           0.12
> >                             &zstrm->lock:             0              0           0.00           0.00           0.00           0.00              0         664129           1.68        1004.80    14853571.32          22.37
> > 
> > PATCHED
> > =======
> > 
> > 1366.50user 154.89system 1:30.33elapsed 1684%CPU (0avgtext+0avgdata 825692maxresident)k
> > 
> > lock stats
> > 
> >                               class name    con-bounces    contentions   waittime-min   waittime-max waittime-total   waittime-avg    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total   holdtime-avg
> >                          &pool->lock#3-R:             0              0           0.00           0.00           0.00           0.00           3648         701979           0.12          44.09      107333.02           0.15
> >                             &class->lock:             0              0           0.00           0.00           0.00           0.00           5038         840434           0.06        1245.90      211814.60           0.25
> >                          zsmalloc-page-R:             0              0           0.00           0.00           0.00           0.00              0         664078           0.05         699.35      236641.75           0.36
> >                         zram-entry->lock:             0              0           0.00           0.00           0.00           0.00              0        3098328           0.06        2987.02      313339.11           0.10
> >    &per_cpu_ptr(comp->stream, cpu)->lock:             0              0           0.00           0.00           0.00           0.00             23         664078           1.77        7071.30    14838397.61          22.34
> 
> So...
> 
> I added lock-stat handling to zspage->lock and to zram (in zram it's only
> trylock that we can track, but it doesn't really bother me).  I also
> renamed zsmalloc-page-R to old zspage->lock-R and zram-entry->lock to
> old zram->table[index].lock, just in case if anyone cares.
> 
> Now bounces stats for zspage->lock and zram->table[index].lock look
> pretty much like in BASE case.
> 
> PATCHED
> =======
> 
>                               class name    con-bounces    contentions   waittime-min   waittime-max waittime-total   waittime-avg    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total   holdtime-avg
>                          &pool->lock#3-R:             0              0           0.00           0.00           0.00           0.00           2702         703841           0.22         873.90      197110.49           0.28
>                             &class->lock:             0              0           0.00           0.00           0.00           0.00           4590         842336           0.10        3329.63      256595.70           0.30
>                           zspage->lock-R:             0              0           0.00           0.00           0.00           0.00           4750         665011           0.08        3360.60      258402.21           0.39
>                  zram->table[index].lock:             0              0           0.00           0.00           0.00           0.00        1722291        3099346           0.12        6943.09      721282.34           0.23
>    &per_cpu_ptr(comp->stream, cpu)->lock:             0              0           0.00           0.00           0.00           0.00             23         665011           2.84        7062.18    14896206.16          22.40
> 

holdtime-max and holdtime-total are higher in the patched kernel. Not
sure if this is just an artifact of lock holders being preemtible.