Re: [Xen-devel] [PATCH] tools/xenconsoled: Increase file descriptor limit

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 16/02/2015 20:44, Don Slutz wrote:
> On 02/16/15 13:17, 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@xxxxxxxxxx>
>> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
>> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
>> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
>> ---
>>  tools/console/daemon/main.c |   31 +++++++++++++++++++++++++++++++
>>  1 file changed, 31 insertions(+)
>>
>> diff --git a/tools/console/daemon/main.c b/tools/console/daemon/main.c
>> index 92d2fc4..759c061 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 +56,34 @@ static void version(char *name)
>>      printf("Xen Console Daemon 3.0\n");
>>  }
>>  
>> +/*
>> + * Xenconsoled requires one file descriptor for each PV console, 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;
>> +    long nr_open = 4096;
>> +    int rc;
>> +
>> +    rc = getrlimit(RLIMIT_NOFILE, &lim);
>> +    if (rc)
>> +            return;
>> +
>> +    fs_nr_open = fopen("/proc/sys/fs/nr_open", "r");
>> +    if (fs_nr_open) {
>> +            fscanf(fs_nr_open, "%ld", &nr_open);
>> +            fclose(fs_nr_open);
>> +    }
>> +
>> +    if ((nr_open > lim.rlim_cur) || (nr_open > lim.rlim_max)) {
>> +            lim.rlim_cur = lim.rlim_max = nr_open;
>> +            setrlimit(RLIMIT_NOFILE, &lim);
>> +    }
>> +}
>> +
> I am not sure that Xenconsoled is required to have the CAP_SYS_RESOURCE
> capability.  With out this, the "soft" (rlim_cur) will most like not be
> changed.  Does it make sense to include:
>
>     lim.rlim_cur = lim.rlim_max;
>     rc = setrlimit(RLIMIT_NOFILE, &lim);
>     if (rc)
>         return;
>
> before "fs_nr_open = fopen(..."?

It probably does make sense, although xenconsoled cannot realistically
run without privilege because of privcmd and /dev/ptmx.

I shall respin.

~Andrew

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