@@ -278,81 +278,53 @@ __get_nprocs_conf (void)
}
weak_alias (__get_nprocs_conf, get_nprocs_conf)
-/* General function to get information about memory status from proc
- filesystem. */
+
+/* Compute (num*mem_unit)/pagesize, but avoid overflowing long int.
+ In practice, mem_unit is never bigger than the page size, so after
+ the first loop it is 1. [In the kernel, it is initialized to
+ PAGE_SIZE in mm/page_alloc.c:si_meminfo(), and then in
+ kernel.sys.c:do_sysinfo() it is set to 1 if unsigned long can
+ represent all the sizes measured in bytes]. */
static long int
-internal_function
-phys_pages_info (const char *format)
+sysinfo_mempages (unsigned long int num, unsigned int mem_unit)
{
- char buffer[8192];
- long int result = -1;
+ unsigned long int ps = __getpagesize ();
- /* If we haven't found an appropriate entry return 1. */
- FILE *fp = fopen ("/proc/meminfo", "rce");
- if (fp != NULL)
+ while (mem_unit > 1 && ps > 1)
{
- /* No threads use this stream. */
- __fsetlocking (fp, FSETLOCKING_BYCALLER);
-
- result = 0;
- /* Read all lines and count the lines starting with the
- string "processor". We don't have to fear extremely long
- lines since the kernel will not generate them. 8192
- bytes are really enough. */
- while (__fgets_unlocked (buffer, sizeof buffer, fp) != NULL)
- if (sscanf (buffer, format, &result) == 1)
- {
- result /= (__getpagesize () / 1024);
- break;
- }
-
- fclose (fp);
+ mem_unit >>= 1;
+ ps >>= 1;
}
-
- if (result == -1)
- /* We cannot get the needed value: signal an error. */
- __set_errno (ENOSYS);
-
- return result;
+ num *= mem_unit;
+ while (ps > 1)
+ {
+ ps >>= 1;
+ num >>= 1;
+ }
+ return num;
}
-
-/* Return the number of pages of physical memory in the system. There
- is currently (as of version 2.0.21) no system call to determine the
- number. It is planned for the 2.1.x series to add this, though.
-
- One possibility to implement it for systems using Linux 2.0 is to
- examine the pseudo file /proc/cpuinfo. Here we have one entry for
- each processor.
-
- But not all systems have support for the /proc filesystem. If it
- is not available we return -1 as an error signal. */
+/* Return the number of pages of total/available physical memory in
+ the system. This used to be done by parsing /proc/meminfo, but
+ that's unnecessarily expensive (and /proc is not always available).
+ The sysinfo syscall provides the same information, and has been
+ available at least since kernel 2.3.48. */
long int
__get_phys_pages (void)
{
- /* XXX Here will come a test for the new system call. */
+ struct sysinfo info;
- return phys_pages_info ("MemTotal: %ld kB");
+ __sysinfo (&info);
+ return sysinfo_mempages (info.totalram, info.mem_unit);
}
weak_alias (__get_phys_pages, get_phys_pages)
-
-/* Return the number of available pages of physical memory in the
- system. There is currently (as of version 2.0.21) no system call
- to determine the number. It is planned for the 2.1.x series to add
- this, though.
-
- One possibility to implement it for systems using Linux 2.0 is to
- examine the pseudo file /proc/cpuinfo. Here we have one entry for
- each processor.
-
- But not all systems have support for the /proc filesystem. If it
- is not available we return -1 as an error signal. */
long int
__get_avphys_pages (void)
{
- /* XXX Here will come a test for the new system call. */
+ struct sysinfo info;
- return phys_pages_info ("MemFree: %ld kB");
+ __sysinfo (&info);
+ return sysinfo_mempages (info.freeram, info.mem_unit);
}
weak_alias (__get_avphys_pages, get_avphys_pages)
new file mode 100644
@@ -0,0 +1,26 @@
+/* Internal declarations for sys/sysinfo.h.
+ Copyright (C) 2015 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#ifndef _INCLUDE_SYS_SYSINFO_H
+#define _INCLUDE_SYS_SYSINFO_H 1
+
+#include_next <sys/sysinfo.h>
+
+extern __typeof (sysinfo) __sysinfo __THROW;
+
+#endif /* sys/sysinfo.h */
@@ -73,7 +73,7 @@ setpgid - setpgid i:ii __setpgid setpgid
sigaltstack - sigaltstack i:PP __sigaltstack sigaltstack
splice EXTRA splice Ci:iPiPii splice
stime - stime i:p stime
-sysinfo EXTRA sysinfo i:p sysinfo
+sysinfo EXTRA sysinfo i:p __sysinfo sysinfo
swapon - swapon i:si __swapon swapon
swapoff - swapoff i:s __swapoff swapoff
tee EXTRA tee Ci:iiii tee
Profiling git's test suite, Linus noted [1] that a disproportionately large amount of time was spent reading /proc/meminfo. This is done by the glibc functions get_phys_pages and get_avphys_pages, but they only need the MemTotal and MemFree fields, respectively. That same information can be obtained with a single syscall, sysinfo, instead of six: open, fstat, mmap, read, close, munmap. While sysinfo also provides more than necessary, it does a lot less work than what the kernel needs to do to provide the entire /proc/meminfo. Both strace -T and in-app microbenchmarks shows that the sysinfo() approach is roughly an order of magnitude faster. sysinfo() is much older than what glibc currently requires, so I don't think there's any reason to keep the old parsing code. Moreover, this makes get_[av]phys_pages work even in the absence of /proc. Linus noted that something as simple as 'bash -c "echo"' would trigger the reading of /proc/meminfo, but gdb says that many more applications than just bash are affected: Starting program: /bin/bash "-c" "echo" Breakpoint 1, __get_phys_pages () at ../sysdeps/unix/sysv/linux/getsysstats.c:283 283 ../sysdeps/unix/sysv/linux/getsysstats.c: No such file or directory. (gdb) bt #0 __get_phys_pages () at ../sysdeps/unix/sysv/linux/getsysstats.c:283 #1 0x00007ffff76d21c5 in posix_sysconf (name=<optimized out>) at ../sysdeps/posix/sysconf.c:634 #2 linux_sysconf (name=<optimized out>) at ../sysdeps/unix/sysv/linux/x86_64/../sysconf.c:136 #3 *__GI___sysconf (name=85) at ../sysdeps/unix/sysv/linux/x86_64/sysconf.c:37 #4 0x00007ffff765b02a in *(int0_t, long double) (b=<optimized out>, n=76, s=18446744073708915495, cmp=0x472e30, arg=0x0) at msort.c:188 #5 0x000000000042210e in ?? () #6 0x000000000042065d in main () So it seems that any application that uses qsort on a moderately sized array will incur this cost (once), which is obviously proportionately more expensive for lots of short-lived processes (such as the git test suite). [1] http://thread.gmane.org/gmane.linux.kernel/2019285 Signed-off-by: Rasmus Villemoes <rv@rasmusvillemoes.dk> * sysdeps/unix/sysv/linux/getsysstats.c (__get_phys_pages): Use sysinfo system call instead of parsing /proc/meminfo. * sysdeps/unix/sysv/linux/getsysstats.c (__get_avphys_pages): Likewise. --- v2: fix linknamespace violations and a few style issues. sysdeps/unix/sysv/linux/getsysstats.c | 88 +++++++++------------------ sysdeps/unix/sysv/linux/include/sys/sysinfo.h | 26 ++++++++ sysdeps/unix/sysv/linux/syscalls.list | 2 +- 3 files changed, 57 insertions(+), 59 deletions(-) create mode 100644 sysdeps/unix/sysv/linux/include/sys/sysinfo.h