svn commit: r207905 - head/sys/vm

[Alan Cox]

Author: alc
Date: Tue May 11 01:29:18 2010
New Revision: 207905
URL: http://svn.freebsd.org/changeset/base/207905

Log:
  Update synchronization annotations for struct vm_page.  Add a comment
  explaining how the setting of PG_WRITEABLE is synchronized.

Modified:
  head/sys/vm/vm_page.h

Modified: head/sys/vm/vm_page.h
==============================================================================
--- head/sys/vm/vm_page.h	Mon May 10 22:21:08 2010	(r207904)
+++ head/sys/vm/vm_page.h	Tue May 11 01:29:18 2010	(r207905)
@@ -112,7 +112,7 @@ struct vm_page {
 	u_short	flags;			/* see below */
 	uint8_t	order;			/* index of the buddy queue */
 	uint8_t pool;
-	u_short cow;			/* page cow mapping count (Q) */
+	u_short cow;			/* page cow mapping count (P) */
 	u_int wire_count;		/* wired down maps refs (P) */
 	short hold_count;		/* page hold count (P) */
 	u_short oflags;			/* page flags (O) */
@@ -122,16 +122,16 @@ struct vm_page {
 	/* so, on normal X86 kernels, they must be at least 8 bits wide */
 #if PAGE_SIZE == 4096
 	u_char	valid;			/* map of valid DEV_BSIZE chunks (O) */
-	u_char	dirty;			/* map of dirty DEV_BSIZE chunks */
+	u_char	dirty;			/* map of dirty DEV_BSIZE chunks (O) */
 #elif PAGE_SIZE == 8192
 	u_short	valid;			/* map of valid DEV_BSIZE chunks (O) */
-	u_short	dirty;			/* map of dirty DEV_BSIZE chunks */
+	u_short	dirty;			/* map of dirty DEV_BSIZE chunks (O) */
 #elif PAGE_SIZE == 16384
 	u_int valid;			/* map of valid DEV_BSIZE chunks (O) */
-	u_int dirty;			/* map of dirty DEV_BSIZE chunks */
+	u_int dirty;			/* map of dirty DEV_BSIZE chunks (O) */
 #elif PAGE_SIZE == 32768
 	u_long valid;			/* map of valid DEV_BSIZE chunks (O) */
-	u_long dirty;			/* map of dirty DEV_BSIZE chunks */
+	u_long dirty;			/* map of dirty DEV_BSIZE chunks (O) */
 #endif
 };
 
@@ -216,6 +216,9 @@ extern struct vpglocks pa_lock[];
  *	 via the object/vm_page_t because there is no knowledge of their
  *	 pte mappings, nor can they be removed from their objects via 
  *	 the object, and such pages are also not on any PQ queue.
+ *
+ * PG_WRITEABLE is set exclusively by pmap_enter().  When it does so, either
+ * the page must be VPO_BUSY or the containing object must be locked.
  */
 #define	PG_CACHED	0x0001		/* page is cached */
 #define	PG_FREE		0x0002		/* page is free */