[PATCH 2/2] Document the M_ARENA_* mallopt parameters

[Siddhesh Poyarekar <siddhesh@sourceware.org>]

The M_ARENA_* mallopt parameters are in wide use in production to
control the number of arenas that a long lived process creates and
hence there is no point in stating that this interface is non-public.
Document this interface and remove the obsolete comment.

	* manual/memory.texi (M_ARENA_TEST): Add documentation.
	(M_ARENA_MAX): Likewise.
	* malloc/malloc.c: Remove obsolete comment.
---
 malloc/malloc.c    |  1 -
 manual/memory.texi | 21 +++++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 09e004b..0011a6d 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -1718,7 +1718,6 @@ static struct malloc_par mp_ =
 };
 
 
-/*  Non public mallopt parameters.  */
 #define M_ARENA_TEST -7
 #define M_ARENA_MAX  -8
 
diff --git a/manual/memory.texi b/manual/memory.texi
index 222f126..b98dcf2 100644
--- a/manual/memory.texi
+++ b/manual/memory.texi
@@ -1153,6 +1153,27 @@ order to return memory to the system.
 
 This parameter can also be set for the process at startup by setting the
 environment variable @code{MALLOC_TRIM_THRESHOLD_} to the desired value.
+
+@item M_ARENA_TEST
+An arena is a memory pool that is allocated to act as a heap alongside the
+system heap that the kernel creates for the process.  This is to provide
+multiple heap structures for multiple threads of a process to reduce contention
+between them.  The limit to the number of such arenas per process is determined
+by the number of cores of the system and whether it is a 32-bit or a 64-bit
+processor.
+
+The value is ignored if @code{M_ARENA_MAX} is set either via @code{mallopt} or
+via the @code{MALLOC_ARENA_MAX} environment variable.
+
+This parameter can also be set for the process at startup by setting the
+environment variable @code{MALLOC_ARENA_TEST} to the desired value.
+
+@item M_ARENA_MAX
+This parameter sets the number of arenas to use regardless of the number of
+cores in the system.
+
+This parameter can also be set for the process at startup by setting the
+environment variable @code{MALLOC_ARENA_MAX} to the desired value.
 @end table
 
 @end deftypefun
-- 
2.7.4