commit 91d5989356325759503311df67e750b358ef4148
Author: Niklas Hambüchen <mail@nh2.me>
Date:   Thu Aug 8 22:02:27 2019 +0200

    malloc: Fix missing accounting of top chunk in malloc_info [BZ #24026]
    
    Fixes `<total type="rest" size="..."> incorrectly showing as 0 most
    of the time.
    
    The rest value being wrong is significant because to compute the
    actual amount of memory handed out via malloc, the user must subtract
    it from <system type="current" size="...">. That result being wrong
    makes investigating memory fragmentation issues like
    <https://bugzilla.redhat.com/show_bug.cgi?id=843478> close to
    impossible.
    
    (cherry picked from commit b6d2c4475d5abc05dd009575b90556bdd3c78ad0)

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 4fc7f175fe42d6c6..fcf480acdaea1b86 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -5433,6 +5433,12 @@ __malloc_info (int options, FILE *fp)
 
       __libc_lock_lock (ar_ptr->mutex);
 
+      /* Account for top chunk.  The top-most available chunk is
+	 treated specially and is never in any bin. See "initial_top"
+	 comments.  */
+      avail = chunksize (ar_ptr->top);
+      nblocks = 1;  /* Top always exists.  */
+
       for (size_t i = 0; i < NFASTBINS; ++i)
 	{
 	  mchunkptr p = fastbin (ar_ptr, i);