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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 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.
27 lines
997 B
C
27 lines
997 B
C
/* Internal declarations for sys/sysinfo.h.
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Copyright (C) 2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _INCLUDE_SYS_SYSINFO_H
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#define _INCLUDE_SYS_SYSINFO_H 1
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#include_next <sys/sysinfo.h>
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extern __typeof (sysinfo) __sysinfo __THROW;
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#endif /* sys/sysinfo.h */
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