Opening a pseudo-tty (/dev/tty[p-zP-T][0-9a-zA-Z]) causes the kernel to
allocate a struct tty for it, as well as ring buffers for tty data. This
memory will not get released if the pseudo-tty is closed, for it may be
opened again in the future.
On pseudo-ttys, the largest possible ring buffer size is used, which
causes 26KB to be allocated (three 8KB rings plus two 1KB quote
buffers).
On a default OpenBSD install, only /dev/tty[pqr][0-9a-zA-Z] are created.
That's 186 ttys. If they were to be opened, this would cause 4836KB of
kernel memory to be allocated.
And that's exactly what ttyflags(8) does: it will happily open every tty
listed in /etc/ttys, and issue a TIOCSFLAGS ioctl to it, then close it.
But pseudo-ttys ignore TIOCSFLAGS completely, so there is no point for
ttyflags to open them, to begin with.
On memory challenged systems, this is a significant waste of memory. I
am therefore proposing the following diff, which will cause ttyflags -a
to skip pseudo-ttys.
Without this diff, after a multiuser boot:
kern.malloc.kmemstat.ttys=(inuse = 1128, calls = 1128, memuse = 4982K,
limblocks = 0, mapblocks = 0, maxused = 4982K, limit = 78644K, spare = 0, sizes
= (512,1024,8192))
With this diff:
kern.malloc.kmemstat.ttys=(inuse = 18, calls = 18, memuse = 80K, limblocks = 0,
mapblocks = 0, maxused = 80K, limit = 78644K, spare = 0, sizes =
(512,1024,8192))
Index: ttyflags.c
===================================================================
RCS file: /OpenBSD/src/sbin/ttyflags/ttyflags.c,v
retrieving revision 1.13
diff -u -p -r1.13 ttyflags.c
--- ttyflags.c 4 Dec 2012 02:27:00 -0000 1.13
+++ ttyflags.c 13 Jan 2019 16:14:59 -0000
@@ -112,9 +112,13 @@ all(int print)
int rval;
rval = 0;
- for (tep = getttyent(); tep != NULL; tep = getttyent())
+ for (tep = getttyent(); tep != NULL; tep = getttyent()) {
+ /* pseudo-tty ignore TIOCSFLAGS, so don't bother */
+ if (strcmp(tep->ty_type, "network") == 0)
+ continue;
if (ttyflags(tep, print))
rval = 1;
+ }
return (rval);
}
