linux-kernel - Re: [PATCH v11 8/8] vhost: use vhost

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Date:   Fri, 5 May 2023 15:40:19 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Mike Christie <michael.christie@...cle.com>, hch@...radead.org,
        stefanha@...hat.com, jasowang@...hat.com, mst@...hat.com,
        sgarzare@...hat.com, virtualization@...ts.linux-foundation.org,
        brauner@...nel.org, ebiederm@...ssion.com,
        torvalds@...ux-foundation.org, konrad.wilk@...cle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 8/8] vhost: use vhost_tasks for worker threads

Le 03/02/2023 à 00:25, Mike Christie a écrit :
> For vhost workers we use the kthread API which inherit's its values from
> and checks against the kthreadd thread. This results in the wrong RLIMITs
> being checked, so while tools like libvirt try to control the number of
> threads based on the nproc rlimit setting we can end up creating more
> threads than the user wanted.
> 
> This patch has us use the vhost_task helpers which will inherit its
> values/checks from the thread that owns the device similar to if we did
> a clone in userspace. The vhost threads will now be counted in the nproc
> rlimits. And we get features like cgroups and mm sharing automatically,
> so we can remove those calls.
> 
> Signed-off-by: Mike Christie <michael.christie@...cle.com>
> Acked-by: Michael S. Tsirkin <mst@...hat.com>

I have a question about (a side effect of?) this patch. The output of the 'ps'
command has changed. Here is an example:

Before:
$ ps
    PID TTY          TIME CMD
    598 ttyS0    00:00:00 login
    640 ttyS0    00:00:00 bash
   8880 ttyS0    00:00:06 example:2
   9389 ttyS0    00:00:00 ps
$ ps a
    PID TTY      STAT   TIME COMMAND
    598 ttyS0    Ss     0:00 /bin/login -p --
    602 tty1     Ss+    0:00 /sbin/agetty -o -p -- \u --noclear tty1 linux
    640 ttyS0    S      0:00 /bin/bash -li
   8880 ttyS0    SLl    0:10 /usr/bin/example
   9396 ttyS0    R+     0:00 ps a
$ pgrep -f example
8880

After:
$ ps
    PID TTY          TIME CMD
    538 ttyS0    00:00:00 login
    574 ttyS0    00:00:00 bash
   8275 ttyS0    00:03:28 example:2
   8285 ttyS0    00:00:00 vhost-8275
   8295 ttyS0    00:00:00 vhost-8275
   8299 ttyS0    00:00:00 vhost-8275
   9054 ttyS0    00:00:00 ps
$ ps a
    PID TTY      STAT   TIME COMMAND
    538 ttyS0    Ss     0:00 /bin/login -p --
    540 tty1     Ss+    0:00 /sbin/agetty -o -p -- \u --noclear tty1 linux
    574 ttyS0    S      0:00 /bin/bash -li
   8275 ttyS0    SLl    3:28 /usr/bin/example
   8285 ttyS0    SL     0:00 /usr/bin/example
   8295 ttyS0    SL     0:00 /usr/bin/example
   8299 ttyS0    SL     0:00 /usr/bin/example
   9055 ttyS0    R+     0:00 ps a
$ pgrep -f example
8275
8285
8295
8299

Is this an intended behavior?
This breaks some of our scripts.


Regards,
Nicolas