xref: /dragonfly/share/man/man9/zone.9 (revision c03f08f3) 
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26.\" $FreeBSD: src/share/man/man9/zone.9,v 1.9.2.4 2002/05/02 20:01:29 asmodai Exp $
27.\" $DragonFly: src/share/man/man9/zone.9,v 1.4 2006/10/19 18:44:00 swildner Exp $
28.\"
29.Dd January 27, 2001
30.Dt ZONE 9
31.Os
32.Sh NAME
33.Nm zbootinit ,
34.Nm zinitna ,
35.Nm zinit ,
36.Nm zalloc ,
37.Nm zfree ,
38.Nd zone allocator
39.Sh SYNOPSIS
40.In sys/param.h
41.In sys/queue.h
42.In vm/vm_zone.h
43.Ft void
44.Fn zbootinit "vm_zone_t z" "char *name" "int size" "void *item" "int nitems"
45.Ft int
46.Fn zinitna "vm_zone_t z" "struct vm_object *obj" "char *name" "int size" "int nentries" "int flags" "int zalloc"
47.Ft vm_zone_t
48.Fn zinit "char *name" "int size" "int nentries" "int flags" "int zalloc"
49.Ft void *
50.Fn zalloc "vm_zone_t z"
51.Ft void
52.Fn zfree "vm_zone_t z" "void *item"
53.Sh DESCRIPTION
54The zone allocator provides an efficient interface for managing
55dynamically-sized collections of items of similar size.
56The zone allocator can work with preallocated zones as well as with
57runtime-allocated ones, and is therefore available much earlier in the
58boot process than other memory management routines.
59.Pp
60A zone is an extensible collection of items of identical size.
61The zone allocator keeps track of which items are in use and which
62are not, and provides functions for allocating items from the zone and
63for releasing them back (which makes them available for later use).
64.Pp
65The zone allocator stores state information inside the items proper
66while they are not allocated,
67so structures that will be managed by the zone allocator
68and wish to use the type stable property of zones by leaving some fields
69pre-filled between allocations, must reserve
70two pointers at the very beginning for internal use by the zone
71allocator, as follows:
72.Bd -literal
73struct my_item {
74        struct my_item  *z_rsvd1;
75        struct my_item  *z_rsvd2;
76        /* rest of structure */
77};
78.Ed
79.Pp
80Alternatively they should assume those entries corrupted
81after each allocation.
82After the first allocation of an item,
83it will have been cleared to zeroes, however subsequent allocations
84will retain the contents as of the last free, with the exception of the
85fields mentioned above.
86.Pp
87Zones are created in one of two fashions, depending how far along the
88boot process is.
89.Pp
90If the VM system is fully initialized, a dynamically allocated zone can
91be created using
92.Fn zinit .
93The
94.Fa name
95argument should be a pointer to a short, descriptive name for the
96zone; it is used for statistics and debugging purposes.
97The
98.Fa size
99and
100.Fa nentries
101are the size of the items held by the zone and the initial size (in
102items) of the zone, respectively.
103The
104.Fa flags
105argument should be set to
106.Dv ZONE_INTERRUPT
107if there is a chance that items may be allocated from the zone in
108interrupt context; note that in this case, the zone will never grow
109larger than
110.Fa nentries
111items.
112In all other cases,
113.Fa flags
114should be set to 0.
115The final argument,
116.Fa zalloc ,
117indicates the number of VM pages by which the zone should grow every
118time it fills up.
119.Pp
120If the VM system is not yet fully initialized, the zone allocator
121cannot dynamically allocate VM pages from which to dole out items, so
122the caller needs to provide a static pool of items.
123In this case, the initialization is done in two stages: first,
124.Fn zbootinit
125is called before first use of the zone; later, when the VM system is
126up, the initialization of the zone is completed by calling
127.Fn zinitna .
128.Pp
129The first argument to
130.Fn zbootinit
131is a pointer to a static
132.Vt "struct vm_zone"
133to initialize.
134The second and third are the name of the zone and the size of the
135items it will hold.
136The fourth argument is a pointer to a static array of items from which
137the zone allocator will draw until the zone is fully initialized.
138The
139.Fa nitems
140argument is the number of items in the array.
141.Pp
142The arguments to
143.Fa zinitna
144are the same as for
145.Fa zinit ,
146with the addition of a pointer to the zone to initialize, and a
147pointer to a
148.Vt "struct vm_object"
149from which to allocate pages in the
150.Dv ZONE_INTERRUPT
151case.
152.Pp
153To allocate an item from a zone, simply call
154.Fn zalloc
155with a pointer to that zone; it will return a pointer to an item, or
156.Dv NULL
157in the rare case where all items in the zone are in use and the
158allocator is unable to grow the zone.
159The
160.Fn zalloc
161and
162.Fn zfree
163functions are interrupt and SMP safe.
164.Pp
165Items are released back to the zone from which they were allocated by
166calling
167.Fn zfree
168with a pointer to the zone and a pointer to the item.
169.Sh RETURN VALUES
170The
171.Fn zinitna
172function returns 1 on success and 0 on failure; the only failure case
173is inability to preallocate address space for an interrupt-safe zone.
174.Pp
175The
176.Fn zinit
177function returns a pointer to a fully initialized
178.Vt "struct vm_zone" ,
179or
180.Dv NULL
181if it was unable to
182.Fn kmalloc
183a
184.Vt "struct vm_zone"
185or the
186.Dv ZONE_INTERRUPT
187flag was specified and
188.Fn zinitna
189failed to preallocate address space.
190.Pp
191The
192.Fn zalloc
193function returns a pointer to an item, or
194.Dv NULL
195if the zone ran out of unused items and the allocator was unable to
196enlarge it.
197.Sh SEE ALSO
198.Xr kmalloc 9
199.Sh HISTORY
200The zone allocator first appeared in
201.Fx 3.0 .
202.Sh AUTHORS
203.An -nosplit
204The zone allocator was written by
205.An John S. Dyson .
206.Pp
207This manual page was written by
208.An Dag-Erling Co\(:idan Sm\(/orgrav Aq des@FreeBSD.org .
209