[libvirt] [PATCH] Increase default task limit for libvirtd

[Daniel P. Berrange]

On Wed, Apr 19, 2017 at 01:29:01PM -0600, Jim Fehlig wrote:
> libvirtd can spawn threads/tasks when creating new domains for
> some hypervisors such as Xen's libxl driver, quickly reaching
> the cgroups pids controller default TasksMax setting of 512. When
> the limit is reached, attempting to create additional domains
> results in an error from the cgroups pids controller, e.g.
> 
> kernel: [71282.213347] cgroup: fork rejected by pids controller in
> /system.slice/libvirtd.service
> 
> Depending on domain type and configuration, anywhere from 4-7
> threads/tasks may be created by libxl when starting a domain.
> In order to support 4096 domains, similar to commit 27cd763500,
> increase the TasksMax setting in libvirtd.service to
> 4096 * 8 = 32768 tasks.
> 
> Signed-off-by: Jim Fehlig <jfehlig at suse.com>
> ---
>  daemon/libvirtd.service.in | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/daemon/libvirtd.service.in b/daemon/libvirtd.service.in
> index 899abdf37..fbaf02f3b 100644
> --- a/daemon/libvirtd.service.in
> +++ b/daemon/libvirtd.service.in
> @@ -29,6 +29,11 @@ Restart=on-failure
>  # If changing this, also consider virtlogd.service & virtlockd.service
>  # limits which are also related to number of guests
>  LimitNOFILE=8192
> +# The cgroups pids controller can limit the number of tasks started by
> +# the daemon, which can limit the number of domains for some hypervisors.
> +# A conservative default of 8 tasks per guest results in a TasksMax of
> +# 32k to support 4096 guests.
> +TasksMax=32768
>  
>  [Install]
>  WantedBy=multi-user.target

ACK


Regards,
Daniel
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