Shrink heap on linux when overcommit_memory == 2

Using madvise with MADV_DONTNEED to release memory back to the kernel
is not sufficient to change the commit charge accounted against the
process on Linux.  It is OK however, when overcommit is enabled or is
heuristic.  However, when overcommit is restricted to a percentage of
memory setting the contents of /proc/sys/vm/overcommit_memory as 2, it
makes a difference since memory requests will fail.  Hence, we do what
we do with secure exec binaries, which is to call mmap on the region
to be dropped with MAP_FIXED. This internally unmaps the pages in
question and reduces the amount of memory accounted against the
process.

1 files changed, 10 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index cfab6264de..46ffa6775e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,15 @@
 2012-09-25  Siddhesh Poyarekar  <siddhesh@redhat.com>
 
+	* malloc/arena.c: Include malloc-sysdep.h.
+	(shrink_heap): Use check_may_shrink_heap to decide if madvise
+	is sufficient to shrink the heap or an unmap is needed.
+	* sysdeps/generic/malloc-sysdep.h: New file.  Define
+	new function check_may_shrink_heap.
+	* sysdeps/unix/sysv/linux/malloc-sysdep.h: New file.  Define
+	new function check_may_shrink_heap.
+
+2012-09-25  Siddhesh Poyarekar  <siddhesh@redhat.com>
+
 	* libio/fileops.c (_IO_new_file_seekoff): Fix typos in
 	comments.