[PATCH 2/3] lib/core/fiber: Mark stack as unneeded on creation

[Cyrill Gorcunov <gorcunov@gmail.com>]

Since we've increased the default stack size we hope
the whole 512K 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 implemented in
another patch series later.

Closes #3418
---
 src/lib/core/fiber.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/lib/core/fiber.c b/src/lib/core/fiber.c
index f16ac873f..a1b261ad4 100644
--- a/src/lib/core/fiber.c
+++ b/src/lib/core/fiber.c
@@ -749,6 +749,14 @@ fiber_stack_create(struct fiber *fiber, size_t stack_size)
 	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 if OS
+	 * allows us.
+	 */
+	madvise(fiber->stack, fiber->stack_size, MADV_DONTNEED);
+#endif
 
 	mprotect(guard, page_size, PROT_NONE);
 	return 0;
-- 
2.20.1