[rfc 2/4] core/fiber: Mark stack as unneeded on creation

[Cyrill Gorcunov <gorcunov@gmail.com>]

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Since we've increased the default stack size we hope
the whole 256K won't be used for regular loads thus
we mark the stack area as unneeded to minimize rss
pressure.

Note we do this on fiber creation at the moment, more
detailed stack usage analisys will be in next patches
since it doesn't depend on this change.

Closes #3418
---
 src/lib/core/fiber.c |    7 +++++++
 1 file changed, 7 insertions(+)

Index: tarantool.git/src/lib/core/fiber.c
===================================================================
--- tarantool.git.orig/src/lib/core/fiber.c
+++ tarantool.git/src/lib/core/fiber.c
@@ -749,6 +749,13 @@ fiber_stack_create(struct fiber *fiber,
 	fiber->stack_id = VALGRIND_STACK_REGISTER(fiber->stack,
 						  (char *)fiber->stack +
 						  fiber->stack_size);
+#ifndef TARGET_OS_DARWIN
+	/*
+	 * We don't expect the whole stack usage in regular
+	 * loads, lets try to minimize rss pressure.
+	 */
+	madvise(fiber->stack, fiber->stack_size, MADV_DONTNEED);
+#endif
 
 	mprotect(guard, page_size, PROT_NONE);
 	return 0;