ZONE(9) BSD Kernel Developer's Manual ZONE(9)NAME
zbootinit, zinitna, zinit, zdestroy, zalloc, zfree, — zone allocator
SYNOPSIS
#include <sys/param.h>
#include <sys/queue.h>
#include <vm/vm_zone.h>
void
zbootinit(vm_zone_t z, char *name, int size, void *item, int nitems);
int
zinitna(vm_zone_t z, struct vm_object *obj, char *name, int size,
int nentries, int flags, int zalloc);
vm_zone_t
zinit(char *name, int size, int nentries, int flags, int zalloc);
void
zdestroy(vm_zone_t z);
void *
zalloc(vm_zone_t z);
void
zfree(vm_zone_t z, void *item);
DESCRIPTION
The zone allocator is deprecated. Use <sys/objcache.h> for new develop‐
ments.
The zone allocator provides an efficient interface for managing dynami‐
cally-sized collections of items of similar size. The zone allocator can
work with preallocated zones as well as with runtime-allocated ones, and
is therefore available much earlier in the boot process than other memory
management routines.
A zone is an extensible collection of items of identical size. The zone
allocator keeps track of which items are in use and which are not, and
provides functions for allocating items from the zone and for releasing
them back (which makes them available for later use).
The zone allocator stores state information inside the items proper while
they are not allocated, so structures that will be managed by the zone
allocator and wish to use the type stable property of zones by leaving
some fields pre-filled between allocations, must reserve two pointers at
the very beginning for internal use by the zone allocator, as follows:
struct my_item {
struct my_item *z_rsvd1;
struct my_item *z_rsvd2;
/* rest of structure */
};
Alternatively they should assume those entries corrupted after each allo‐
cation. After the first allocation of an item, it will have been cleared
to zeroes, however subsequent allocations will retain the contents as of
the last free, with the exception of the fields mentioned above.
Zones are created in one of two fashions, depending how far along the
boot process is.
If the VM system is fully initialized, a dynamically allocated zone can
be created using zinit(). The name argument should be a pointer to a
short, descriptive name for the zone; it is used for statistics and
debugging purposes. The size and nentries are the size of the items held
by the zone and the initial size (in items) of the zone, respectively.
The flags argument should have the ZONE_INTERRUPT bit set if there is a
chance that items may be allocated from the zone in interrupt context;
note that in this case, the zone will never grow larger than nentries
items. The flags argument should have the ZONE_DESTROYABLE bit set if
the zone is to be destroyed with zdestroy(). The final argument, zalloc,
indicates the number of VM pages by which the zone should grow every time
it fills up.
If the VM system is not yet fully initialized, the zone allocator cannot
dynamically allocate VM pages from which to dole out items, so the caller
needs to provide a static pool of items. In this case, the initializa‐
tion is done in two stages: first, zbootinit() is called before first use
of the zone; later, when the VM system is up, the initialization of the
zone is completed by calling zinitna().
The first argument to zbootinit() is a pointer to a static struct vm_zone
to initialize. The second and third are the name of the zone and the
size of the items it will hold. The fourth argument is a pointer to a
static array of items from which the zone allocator will draw until the
zone is fully initialized. The nitems argument is the number of items in
the array.
The arguments to zinitna are the same as for zinit, with the addition of
a pointer to the zone to initialize, and a pointer to a struct vm_object
from which to allocate pages in the ZONE_INTERRUPT case.
To release all the memory allocated for a zone, call zdestroy(). Only
zones created with zinit() and with the ZONE_DESTROYABLE flag can be
destroyed.
To allocate an item from a zone, simply call zalloc() with a pointer to
that zone; it will return a pointer to an item, or NULL in the rare case
where all items in the zone are in use and the allocator is unable to
grow the zone.
Items are released back to the zone from which they were allocated by
calling zfree() with a pointer to the zone and a pointer to the item.
The zone functions are not SMP-safe. The MP lock must be held while
calling them.
RETURN VALUES
The zinitna() function returns 1 on success and 0 on failure; the only
failure case is inability to preallocate address space for an interrupt-
safe zone.
The zinit() function returns a pointer to a fully initialized struct
vm_zone, or NULL if it was unable to kmalloc() a struct vm_zone or the
ZONE_INTERRUPT flag was specified and zinitna() failed to preallocate
address space.
The zalloc() function returns a pointer to an item, or NULL if the zone
ran out of unused items and the allocator was unable to enlarge it.
SEE ALSOmemory(9)HISTORY
The zone allocator first appeared in FreeBSD 3.0.
AUTHORS
The zone allocator was written by John S. Dyson.
This manual page was written by Dag-Erling Coïdan Smørgrav
⟨des@FreeBSD.org⟩.
BSD January 27, 2001 BSD
