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Хостинг:
uma_zcreate uma_zalloc uma_zalloc_arg uma_zfree uma_zfree_arg uma_zdestroy uma_zone_set_max - zone allocator
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).
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.
The
uma_zcreate ();
function creates a new zone from which items may then be allocated from.
The
Fa name
argument is a text name of the zone for debugging and stats; this memory
should not be freed until the zone has been deallocated.
The
Fa ctor
and
Fa dtor
arguments are callback functions that are called by
the uma subsystem at the time of the call to
uma_zalloc ();
and
uma_zfree ();
respectively.
Their purpose is to provide hooks for initializing or
destroying things that need to be done at the time of the allocation
or release of a resource.
A good usage for the
Fa ctor
and
Fa dtor
callbacks
might be to adjust a global count of the number of objects allocated.
The
Fa uminit
and
Fa fini
arguments are used to optimize the allocation of
objects from the zone.
They are called by the uma subsystem whenever
it needs to allocate or free several items to satisfy requests or memory
pressure.
A good use for the
Fa uminit
and
Fa fini
callbacks might be to
initialize and destroy mutexes contained within the object.
This would
allow one to re-use already initialized mutexes when an object is returned
from the uma subsystem's object cache.
They are not called on each call to
uma_zalloc ();
and
uma_zfree ();
but rather in a batch mode on several objects.
To allocate an item from a zone, simply call
uma_zalloc ();
with a pointer to that zone
and set the
Fa flags
argument to selected flags as documented in
malloc(9).
It will return a pointer to an item if successful,
or
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
M_NOWAIT
is specified.
Items are released back to the zone from which they were allocated by
calling
uma_zfree ();
with a pointer to the zone and a pointer to the item.
The variations
uma_zalloc_arg ();
and
uma_zfree_arg ();
allow to
specify an argument for the
ctor
and
dtor
functions, respectively.
Created zones,
which are empty,
can be destroyed using
uma_zdestroy (,);
freeing all memory that was allocated for the zone.
All items allocated from the zone with
uma_zalloc ();
must have been freed with
uma_zfree ();
before.
The purpose of
uma_zone_set_max ();
is to limit the maximum amount of memory that the system can dedicated
toward the zone specified by the
Fa zone
argument.
The
Fa nitems
argument gives the upper limit of items in the zone.
This limits the total number of items in the zone which includes:
allocated items, free items and free items in the per-cpu caches.
On systems with more than one CPU it may not be possible to allocate
the specified number of items even when there is no shortage of memory,
because all of the remaining free items may be in the caches of the
other CPUs when the limit is hit.
This manual page was written by An Dag-Erling Sm/orgrav Aq des@FreeBSD.org . Changes for UMA by An Jeroen Ruigrok van der Werven Aq asmodai@FreeBSD.org .
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