svn commit: r332572 - stable/11/sys/vm

[Gleb Smirnoff]

Author: glebius
Date: Mon Apr 16 15:07:19 2018
New Revision: 332572
URL: https://svnweb.freebsd.org/changeset/base/332572

Log:
  Merge r331871:
    Handle a special case when a slab can fit only one allocation,
    and zone has a large alignment. With alignment taken into
    account uk_rsize will be greater than space in a slab. However,
    since we have only one item per slab, it is always naturally
    aligned.
  
    Code that will panic before this change with 4k page:
  
          z = uma_zcreate("test", 3984, NULL, NULL, NULL, NULL, 31, 0);
          uma_zalloc(z, M_WAITOK);
  
    A practical scenario to hit the panic is a machine with 56 CPUs
    and 2 NUMA domains, which yields in zone size of 3984 (on head).
  
  PR:		227116

Modified:
  stable/11/sys/vm/uma_core.c
Directory Properties:
  stable/11/   (props changed)

Modified: stable/11/sys/vm/uma_core.c
==============================================================================
--- stable/11/sys/vm/uma_core.c	Mon Apr 16 14:46:02 2018	(r332571)
+++ stable/11/sys/vm/uma_core.c	Mon Apr 16 15:07:19 2018	(r332572)
@@ -1249,7 +1249,15 @@ keg_small_init(uma_keg_t keg)
 	else 
 		shsize = sizeof(struct uma_slab);
 
-	keg->uk_ipers = (slabsize - shsize) / rsize;
+	if (rsize <= slabsize - shsize)
+		keg->uk_ipers = (slabsize - shsize) / rsize;
+	else {
+		/* Handle special case when we have 1 item per slab, so
+		 * alignment requirement can be relaxed. */
+		KASSERT(keg->uk_size <= slabsize - shsize,
+		    ("%s: size %u greater than slab", __func__, keg->uk_size));
+		keg->uk_ipers = 1;
+	}
 	KASSERT(keg->uk_ipers > 0 && keg->uk_ipers <= SLAB_SETSIZE,
 	    ("%s: keg->uk_ipers %u", __func__, keg->uk_ipers));