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Message-ID: <aba6cca4-e66c-768f-375c-b38c8ba5e8a8@6wind.com>
Date:   Fri, 5 May 2023 15:40:19 +0200
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Reply-To: nicolas.dichtel@6wind.com
Subject: Re: [PATCH v11 8/8] vhost: use vhost_tasks for worker threads
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To:     Mike Christie <michael.christie@oracle.com>, hch@infradead.org,
        stefanha@redhat.com, jasowang@redhat.com, mst@redhat.com,
        sgarzare@redhat.com, virtualization@lists.linux-foundation.org,
        brauner@kernel.org, ebiederm@xmission.com,
        torvalds@linux-foundation.org, konrad.wilk@oracle.com,
        linux-kernel@vger.kernel.org
References: <20230202232517.8695-1-michael.christie@oracle.com>
 <20230202232517.8695-9-michael.christie@oracle.com>
From:   Nicolas Dichtel <nicolas.dichtel@6wind.com>
Organization: 6WIND
In-Reply-To: <20230202232517.8695-9-michael.christie@oracle.com>
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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@oracle.com>
> Acked-by: Michael S. Tsirkin <mst@redhat.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