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$FreeBSD: head/share/man/man9/zone.9 95798 2002-04-30 14:26:22Z asmodai $
.Dd January 27, 2001 .Dt ZONE 9 .Os .Sh NAME .Nm uma_zalloc , .Nm uma_zfree , .Nm uma_zdestroy .Nd zone allocator .Sh SYNOPSIS n sys/param.h n sys/queue.h n vm/uma.h .Ft void * .Fn uma_zalloc "uma_zone_t zone, int wait" .Ft void .Fn uma_zfree "uma_zone_t zone" "void *item" .Ft void .Fn uma_zdestroy "uma_zone_t zone" .Sh DESCRIPTION The zone allocator provides an efficient interface for managing dynamically-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.
p 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).
p 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: d -literal struct my_item { struct my_item *z_rsvd1; struct my_item *z_rsvd2; /* rest of structure */ }; .Ed
p Alternatively they should assume those entries corrupted after each allocation. 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.
p To allocate an item from a zone, simply call .Fn uma_zalloc with a pointer to that zone and set the .Fa wait argument to .Dv M_WAITOK or .Dv M_NOWAIT depending on whether or not to block while allocating memory for this zone, should we run out. It will return a pointer to an item if successful, or .Dv NULL in the rare case where all items in the zone are in use and the allocator is unable to grow the zone or when .Dv M_NOWAIT is specified.
p Items are released back to the zone from which they were allocated by calling .Fn uma_zfree with a pointer to the zone and a pointer to the item.
p Zones created with .Fn zinit can be destroyed using .Fn uma_zdestroy , freeing all memory that was allocated for the zone. All items allocated from the zone with .Fn uma_zalloc must have been freed with .Fn uma_zfree before. .Sh RETURN VALUES
p The .Fn zinit function returns a pointer to a fully initialized .Vt "struct vm_zone" , or .Dv NULL if it was unable to .Fn malloc a .Vt "struct vm_zone" .
p The .Fn uma_zalloc function returns a pointer to an item, or .Dv NULL if the zone ran out of unused items and the allocator was unable to enlarge it. .Sh SEE ALSO .Xr malloc 9 .Sh HISTORY The zone allocator first appeared in .Fx 3.0 . .Sh AUTHORS .An -nosplit The zone allocator was written by .An John S. Dyson .
p This manual page was written by .An Dag-Erling Co\(:idan Sm\(/orgrav Aq des@FreeBSD.org .