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authorDenys Vlasenko2014-11-26 15:17:59 +0100
committerDenys Vlasenko2014-11-26 15:17:59 +0100
commit04c14176023c65550fd46c2e44a1aa04d426d69a (patch)
tree71ac5af09a5303ba891b28bc879a10e1da92c6dc /include
parent2835a224cd603489ac08625265d383d4690cb58a (diff)
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busybox-04c14176023c65550fd46c2e44a1aa04d426d69a.tar.gz
libbb: use ARG_MAX for bb_arg_max() only if it's 60k+
Sometimes ARG_MAX is small (like 32k) yet sysconf(_SC_ARG_MAX) is big, and people prefer using the bigger value. OTOH, with sufficiently large ARG_MAX, further wins from sysconf(_SC_ARG_MAX) being bigger are exponentially smaller: you can see 4 times fewer fork+execs when you run find, but when each execed process already takes a thousand parameters it's likely execution time is dominated by what that process does with each parameter. Thus, with this change ARG_MAX is used if it's sufficiently big, otherwise sysconf(_SC_ARG_MAX) is used. Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'include')
-rw-r--r--include/libbb.h7
1 files changed, 5 insertions, 2 deletions
diff --git a/include/libbb.h b/include/libbb.h
index cc2bea3..17a0089 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -731,11 +731,14 @@ extern void *xmalloc_open_read_close(const char *filename, size_t *maxsz_p) FAST
/* Never returns NULL */
extern void *xmalloc_xopen_read_close(const char *filename, size_t *maxsz_p) FAST_FUNC RETURNS_MALLOC;
-#if defined ARG_MAX
+#if defined(ARG_MAX) && (ARG_MAX >= 60*1024 || !defined(_SC_ARG_MAX))
+/* Use _constant_ maximum if: defined && (big enough || no variable one exists) */
# define bb_arg_max() ((unsigned)ARG_MAX)
-#elif defined _SC_ARG_MAX
+#elif defined(_SC_ARG_MAX)
+/* Else use variable one (a bit more expensive) */
unsigned bb_arg_max(void) FAST_FUNC;
#else
+/* If all else fails */
# define bb_arg_max() ((unsigned)(32 * 1024))
#endif
unsigned bb_clk_tck(void) FAST_FUNC;