[Powertop] [PATCH 02/10] set open files rlimit to /proc/sys/fs/nr_open

From: Jaroslav Skarvada <jskarvad(a)redhat.com&gt; From: Jaroslav Skarvada <jskarvad(a)redhat.com&gt; we have noticed that it can only overcome soft limits, but not hard limits. E.g. on Fedora (and probably others) there is a soft limit of 1024 and a hard limit of 4096, so if powertop opens at least 15 file descriptors per CPU, then this will fail on a system with >273 CPUs. On my system NR_OPEN is 1024, but /proc/sys/fs/nr_open gives me 1048576. It seems the linux kernel hardcodes 1024 * 1024 as the default kernel limit. This default limit can be raised to: sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG; which is 2 Gi - 63 on my 64 bit system. I think we shouldn't touch/increase this. It seems there is no header definition for these limits. I am proposing new patch, which reads the current kernel limit from the /proc. I am not sure about the portability, but at least it shouldn't break anything. Finally I think, the first patch could be applied together with this patch (probably with the changed message) to notify user that he/she reached the FDs limit, because there is still some limit. This could also occur if some process would decrease the /proc/sys/fs/nr_open after it is read by powertop and before the ulimit is set patch merge modifications by: Sergey Senozhatsky <sergey.senozhatsky(a)gmail.com&gt; --- src/main.cpp | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/src/main.cpp b/src/main.cpp index 501a364..4e34ee6 100644 --- a/src/main.cpp +++ b/src/main.cpp @@ -28,6 +28,7 @@ * Arjan van de Ven <arjan(a)linux.intel.com&gt; */ #include <iostream> +#include <fstream> #include <stdlib.h> #include <stdio.h> #include <time.h> @@ -61,6 +62,8 @@ #define DEBUGFS_MAGIC 0x64626720 +#define NR_OPEN_DEF 1024 * 1024 + int debug_learning = 0; unsigned time_out = 20; int leave_powertop = 0; @@ -281,6 +284,20 @@ static void checkroot() { } +static int get_nr_open(void) { + int nr_open = NR_OPEN_DEF; + ifstream file; + + file.open("/proc/sys/fs/nr_open", ios::in); + if (file) { + file >> nr_open; + if (!file) + nr_open = NR_OPEN_DEF; + file.close(); + } + return nr_open; +} + static void powertop_init(void) { static char initialized = 0; @@ -293,8 +310,7 @@ static void powertop_init(void) checkroot(); - getrlimit (RLIMIT_NOFILE, &rlmt); - rlmt.rlim_cur = rlmt.rlim_max; + rlmt.rlim_cur = rlmt.rlim_max = get_nr_open(); setrlimit (RLIMIT_NOFILE, &rlmt); ret = system("/sbin/modprobe cpufreq_stats > /dev/null 2>&1"); -- 1.8.4.679.g0a1a803