svn commit: r240097 - in stable/9/sys: amd64/include boot/common i386/include

[Dag-Erling Smørgrav]

Author: des
Date: Tue Sep  4 19:14:57 2012
New Revision: 240097
URL: http://svn.freebsd.org/changeset/base/240097

Log:
  MFH (r239255, r239730): increase maxswzone on i386 and remove it on amd64.

Modified:
  stable/9/sys/amd64/include/param.h
  stable/9/sys/boot/common/loader.8
  stable/9/sys/i386/include/param.h
Directory Properties:
  stable/9/sys/   (props changed)
  stable/9/sys/boot/   (props changed)

Modified: stable/9/sys/amd64/include/param.h
==============================================================================
--- stable/9/sys/amd64/include/param.h	Tue Sep  4 19:04:02 2012	(r240096)
+++ stable/9/sys/amd64/include/param.h	Tue Sep  4 19:14:57 2012	(r240097)
@@ -123,14 +123,6 @@
 #define	KSTACK_GUARD_PAGES 1	/* pages of kstack guard; 0 disables */
 
 /*
- * Ceiling on amount of swblock kva space, can be changed via
- * the kern.maxswzone /boot/loader.conf variable.
- */
-#ifndef VM_SWZONE_SIZE_MAX
-#define	VM_SWZONE_SIZE_MAX	(32 * 1024 * 1024)
-#endif
-
-/*
  * Mach derived conversion macros
  */
 #define	round_page(x)	((((unsigned long)(x)) + PAGE_MASK) & ~(PAGE_MASK))

Modified: stable/9/sys/boot/common/loader.8
==============================================================================
--- stable/9/sys/boot/common/loader.8	Tue Sep  4 19:04:02 2012	(r240096)
+++ stable/9/sys/boot/common/loader.8	Tue Sep  4 19:14:57 2012	(r240097)
@@ -613,17 +613,26 @@ Not all architectures use such buffers; 
 for details.
 .It Va kern.maxswzone
 Limits the amount of KVM to be used to hold swap
-meta information, which directly governs the
-maximum amount of swap the system can support.
-This value is specified in bytes of KVA space
-and defaults to 32MBytes on i386 and amd64.
-Care should be taken
-to not reduce this value such that the actual
-amount of configured swap exceeds 1/2 the
-kernel-supported swap.
-The default of 32MB allows
-the kernel to support a maximum of ~7GB of swap.
-Only change
+metadata, which directly governs the
+maximum amount of swap the system can support,
+at the rate of approximately 200 MB of swap space
+per 1 MB of metadata.
+This value is specified in bytes of KVA space.
+If no value is provided, the system allocates
+enough memory to handle an amount of swap
+that corresponds to eight times the amount of
+physical memory present in the system.
+.Pp
+Note that swap metadata can be fragmented,
+which means that the system can run out of
+space before it reaches the theoretical limit.
+Therefore, care should be taken to not configure
+more swap than approximately half of the
+theoretical maximum.
+.Pp
+Running out of space for swap metadata can leave
+the system in an unrecoverable state.
+Therefore, you should only change
 this parameter if you need to greatly extend the
 KVM reservation for other resources such as the
 buffer cache or

Modified: stable/9/sys/i386/include/param.h
==============================================================================
--- stable/9/sys/i386/include/param.h	Tue Sep  4 19:04:02 2012	(r240096)
+++ stable/9/sys/i386/include/param.h	Tue Sep  4 19:14:57 2012	(r240097)
@@ -125,9 +125,15 @@
 /*
  * Ceiling on amount of swblock kva space, can be changed via
  * the kern.maxswzone /boot/loader.conf variable.
+ *
+ * 276 is sizeof(struct swblock), but we do not always have a definition
+ * in scope for struct swblock, so we have to hardcode it.  Each struct
+ * swblock holds metadata for 32 pages, so in theory, this is enough for
+ * 16 GB of swap.  In practice, however, the usable amount is considerably
+ * lower due to fragmentation.
  */
 #ifndef VM_SWZONE_SIZE_MAX
-#define VM_SWZONE_SIZE_MAX	(32 * 1024 * 1024)
+#define VM_SWZONE_SIZE_MAX	(276 * 128 * 1024)
 #endif
 
 /*