Improve documentation of 'malloc-trim'

* src/alloc.c (Fmalloc_trim): Fix the doc string.

* etc/NEWS: Document which systems support 'malloc-trim'.

2 files changed, 6 insertions, 5 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 371fbc2145a..fc7432669c3 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1547,7 +1547,8 @@ functions.
 ---
 ** New function 'malloc-trim'.
 This function allows returning unused memory back to the operating
-system, and is mainly meant as a debugging tool.
+system, and is mainly meant as a debugging tool.  It is currently
+available only when Emacs was built with glibc as the C library.
 
 ---
 ** 'x-show-tip' no longer hard-codes a timeout default.
diff --git a/src/alloc.c b/src/alloc.c
index 661f37dd5cc..43fbbb79bed 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -7481,14 +7481,14 @@ arenas.  */)
 
 #ifdef HAVE_MALLOC_TRIM
 DEFUN ("malloc-trim", Fmalloc_trim, Smalloc_trim, 0, 1, "",
-       doc: /* Release free memory from the heap.
-This function asks libc to return unused memory back to the operating
+       doc: /* Release free heap memory to the OS.
+This function asks libc to return unused heap memory back to the operating
 system.  This function isn't guaranteed to do anything, and is mainly
 meant as a debugging tool.
 
 If LEAVE_PADDING is given, ask the system to leave that much unused
-spaced in the heap.  This should be an integer, and if not given,
-defaults to 0.
+space in the heap of the Emacs process.  This should be an integer, and if
+not given, it defaults to 0.
 
 This function returns nil if no memory could be returned to the
 system, and non-nil if some memory could be returned.  */)