Re: [PATCH v3] tools/xenconsoled: Increase file descriptor limit

[Don Slutz <dslutz@verizon.com>]

On 02/17/15 12:55, Andrew Cooper wrote:
> XenServer's VM density testing uncovered a regression when moving from
> sysvinit to systemd where the file descriptor limit dropped from 4096 to
> 1024. (XenServer had previously inserted a ulimit statement into its
> initscripts.)
> 
> One solution is to use LimitNOFILE=4096 in xenconsoled.service to match the
> lost ulimit, but that is only a stopgap solution.
> 
> As Xenconsoled genuinely needs a large number of file descriptors if a large
> number of domains are running, and is well behaved with its descriptors,
> attempt to up the limit to the system maximum.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> CC: Ian Campbell <Ian.Campbell@citrix.com>
> CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
> CC: Wei Liu <wei.liu2@citrix.com>
> 

For what it is worth:

Reviewed-by: Don Slutz <dslutz@verizon.com>

   -Don Slutz

> ---
> v3:
>  * Hide Linux specific bits in #ifdef __linux__
> v2:
>  * Always increase soft limit to hard limit
>  * Correct commment regarding number of file descriptors
>  * long -> unsigned long as that appears to be the underlying type of an rlim_t
> ---
>  tools/console/daemon/main.c |   47 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 47 insertions(+)
> 
> diff --git a/tools/console/daemon/main.c b/tools/console/daemon/main.c
> index 92d2fc4..20ffe6b 100644
> --- a/tools/console/daemon/main.c
> +++ b/tools/console/daemon/main.c
> @@ -26,6 +26,7 @@
>  #include <string.h>
>  #include <signal.h>
>  #include <sys/types.h>
> +#include <sys/resource.h>
>  
>  #include "xenctrl.h"
>  
> @@ -55,6 +56,50 @@ static void version(char *name)
>  	printf("Xen Console Daemon 3.0\n");
>  }
>  
> +/*
> + * Xenconsoled requires two file descriptors for each PV console (pty and log
> + * file), which can easily exceed the default of 1024 if many guests are
> + * running.  Try to set the fd limit to the system maximum, falling back to a
> + * default of 4096.
> + */
> +static void increase_fd_limit(void)
> +{
> +	FILE *fs_nr_open;
> +	struct rlimit lim;
> +	unsigned long nr_open = 4096;
> +
> +	if (getrlimit(RLIMIT_NOFILE, &lim) < 0)
> +		return;
> +
> +	/* Increase the soft limit to the current hard limit. */
> +	if (lim.rlim_cur < lim.rlim_max) {
> +		lim.rlim_cur = lim.rlim_max;
> +		if (setrlimit(RLIMIT_NOFILE, &lim) < 0)
> +			return;
> +	}
> +
> +#ifdef __linux__
> +	/* Attempt to locate the system maximum. */
> +	fs_nr_open = fopen("/proc/sys/fs/nr_open", "r");
> +	if (fs_nr_open) {
> +		unsigned long nr;
> +
> +		if (fscanf(fs_nr_open, "%lu", &nr) == 1)
> +			nr_open = nr;
> +		fclose(fs_nr_open);
> +	}
> +#endif
> +
> +	/*
> +	 * In the likely case that we are a root process with
> +	 * CAP_SYS_RESOURCE, attempt to up our hard limit.
> +	 */
> +	if (nr_open > lim.rlim_max) {
> +		lim.rlim_cur = lim.rlim_max = nr_open;
> +		setrlimit(RLIMIT_NOFILE, &lim);
> +	}
> +}
> +
>  int main(int argc, char **argv)
>  {
>  	const char *sopts = "hVvit:o:";
> @@ -154,6 +199,8 @@ int main(int argc, char **argv)
>  	openlog("xenconsoled", syslog_option, LOG_DAEMON);
>  	setlogmask(syslog_mask);
>  
> +	increase_fd_limit();
> +
>  	if (!is_interactive) {
>  		daemonize(pidfile ? pidfile : "/var/run/xenconsoled.pid");
>  	}
>