I don't think the current man page has enough detail for what the malloc.conf settings do.
Index: lib/libc/stdlib/malloc.3 =================================================================== RCS file: /cvs/src/lib/libc/stdlib/malloc.3,v retrieving revision 1.78 diff -u -p -d -r1.78 malloc.3 --- lib/libc/stdlib/malloc.3 1 May 2014 18:41:59 -0000 1.78 +++ lib/libc/stdlib/malloc.3 11 Jul 2014 04:30:37 -0000 @@ -220,10 +220,16 @@ Malloc will first look for a symbolic li .Pa /etc/malloc.conf and next check the environment for a variable called .Ev MALLOC_OPTIONS +(if not +.Xr issetugid 2 ) and finally for the global variable .Va malloc_options and scan them for flags in that order. Flags are single letters, uppercase means on, lowercase means off. + +The default flags are 'AP', small chunks are always junked, and the first +part of the pages is junked after free. The default junk behavior does not +correspond to 'j' or 'J'. .Bl -tag -width indent .It Cm A .Dq Abort . @@ -270,7 +276,7 @@ Fill some junk into the area allocated. Currently junk is bytes of 0xd0 when allocating; this is pronounced .Dq Duh . \&:-) -Freed chunks are filled with 0xdf. +Freed chunks are filled with 0xdf. This performs more junking than by default. .It Cm j .Dq Don't Junk . By default, small chunks are always junked, and the first part of pages @@ -297,6 +303,7 @@ This can substantially aid in compacting .\"Consult the source for this one. .It Cm S Enable all options suitable for security auditing. +This currently enables flags 'UJG' and sets the free cache page size to 0. .It Cm U .Dq Free unmap . Enable use after free protection for larger allocations.
