[src/trunk]: src/sys/uvm Elaborate on locking scheme and vm_page states.

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/b360e8e49920
branches:  trunk
changeset: 806954:b360e8e49920
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sat Mar 21 13:11:14 2015 +0000

description:
Elaborate on locking scheme and vm_page states.

diffstat:

 sys/uvm/uvm_page.h |  71 ++++++++++++++++++++++++++++++++++++++++-------------
 1 files changed, 53 insertions(+), 18 deletions(-)

diffs (108 lines):

diff -r 761d6513570a -r b360e8e49920 sys/uvm/uvm_page.h
--- a/sys/uvm/uvm_page.h        Sat Mar 21 05:50:19 2015 +0000
+++ b/sys/uvm/uvm_page.h        Sat Mar 21 13:11:14 2015 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: uvm_page.h,v 1.76 2013/10/25 14:30:21 martin Exp $     */
+/*     $NetBSD: uvm_page.h,v 1.77 2015/03/21 13:11:14 riastradh Exp $  */
 
 /*
  * Copyright (c) 1997 Charles D. Cranor and Washington University.
@@ -98,36 +98,71 @@
  *
  * Field markings and the corresponding locks:
  *
- * o:  page owner's lock (UVM object or amap/anon)
- * p:  lock on the page queues
- * o|p:        either lock can be acquired
- * o&p:        both locks are required
+ * f:  free page queue lock, uvm_fpageqlock
+ * o:  page owner (uvm_object::vmobjlock, vm_amap::am_lock, vm_anon::an_lock)
+ * p:  page queue lock, uvm_pageqlock
+ * o,p:        o|p for read, o&p for write
+ * w:  wired page queue or uvm_pglistalloc:
+ *       => wired page queue: o&p to change, stable from wire to unwire
+ *             XXX What about concurrent or nested wire?
+ *       => uvm_pglistalloc: owned by caller
  * ?:  locked by pmap or assumed page owner's lock
  *
  * UVM and pmap(9) may use uvm_page_locked_p() to assert whether the
  * page owner's lock is acquired.
+ *
+ * A page can be in one of four life states:
+ *
+ * o free
+ *   => pageq.list is entry on global free page queue
+ *   => listq.list is entry on per-CPU free page queue
+ *   => uanon is unused (or (void *)0xdeadbeef for DEBUG)
+ *   => uobject is unused (or (void *)0xdeadbeef for DEBUG)
+ *   => PQ_FREE is set in pqflags
+ * o owned by a uvm_object
+ *   => pageq.queue is entry on wired page queue, if any
+ *   => listq.queue is entry on list of pages in object
+ *   => uanon is NULL
+ *   => uobject is owner
+ * o owned by a vm_anon
+ *   => pageq is unused (XXX correct?)
+ *   => listq is unused (XXX correct?)
+ *   => uanon is owner
+ *   => uobject is NULL
+ *   => PQ_ANON is set in pqflags
+ * o allocated by uvm_pglistalloc
+ *   => pageq.queue is entry on resulting pglist, owned by caller
+ *   => listq is unused (XXX correct?)
+ *   => uanon is unused
+ *   => uobject is unused
+ *
+ * The following transitions are allowed:
+ *
+ * - uvm_pagealloc: free -> owned by a uvm_object/vm_anon
+ * - uvm_pagefree: owned by a uvm_object/vm_anon -> free
+ * - uvm_pglistalloc: free -> allocated by uvm_pglistalloc
+ * - uvm_pglistfree: allocated by uvm_pglistalloc -> free
  */
 
 struct vm_page {
        struct rb_node          rb_node;        /* o: tree of pages in obj */
 
        union {
-               TAILQ_ENTRY(vm_page) queue;
-               LIST_ENTRY(vm_page) list;
-       } pageq;                                /* p: queue info for FIFO
-                                                * queue or free list */
+               TAILQ_ENTRY(vm_page) queue;     /* w: wired page queue
+                                                * or uvm_pglistalloc output */
+               LIST_ENTRY(vm_page) list;       /* f: global free page queue */
+       } pageq;
+
        union {
-               TAILQ_ENTRY(vm_page) queue;
-               LIST_ENTRY(vm_page) list;
-       } listq;                                /* o: pages in same object */
+               TAILQ_ENTRY(vm_page) queue;     /* o: pages in same object */
+               LIST_ENTRY(vm_page) list;       /* f: CPU free page queue */
+       } listq;
 
        struct vm_anon          *uanon;         /* o,p: anon */
        struct uvm_object       *uobject;       /* o,p: object */
        voff_t                  offset;         /* o,p: offset into object */
        uint16_t                flags;          /* o: object flags */
-       uint16_t                loan_count;     /* number of active loans
-                                                * o|p: for reading
-                                                * o&p: for modification */
+       uint16_t                loan_count;     /* o,p: num. active loans */
        uint16_t                wire_count;     /* p: wired down map refs */
        uint16_t                pqflags;        /* p: page queue flags */
        paddr_t                 phys_addr;      /* physical address of page */
@@ -149,9 +184,9 @@
  *
  * Locking notes:
  *
- * PG_, struct vm_page::flags  => locked by the owner
- * PQ_, struct vm_page::pqflags        => locked by the page-queue lock
- * PQ_FREE                     => additionally locked by free-queue lock
+ * PG_, struct vm_page::flags  => locked by owner
+ * PQ_, struct vm_page::pqflags        => locked by uvm_pageqlock
+ * PQ_FREE                     => additionally locked by uvm_fpageqlock
  *
  * Flag descriptions:
  *