svn commit: r331871 - head/sys/vm

[Gleb Smirnoff]

Author: glebius
Date: Mon Apr  2 05:11:59 2018
New Revision: 331871
URL: https://svnweb.freebsd.org/changeset/base/331871

Log:
  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.
  
  PR:		227116
  MFC after:	2 weeks

Modified:
  head/sys/vm/uma_core.c

Modified: head/sys/vm/uma_core.c
==============================================================================
--- head/sys/vm/uma_core.c	Sun Apr  1 22:59:53 2018	(r331870)
+++ head/sys/vm/uma_core.c	Mon Apr  2 05:11:59 2018	(r331871)
@@ -1290,7 +1290,15 @@ 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));