VMEM(9)                NetBSD Kernel Developer's Manual                VMEM(9)

NAME
     vmem -- virtual memory allocator

SYNOPSIS
     #include <sys/vmem.h>

     vmem_t *
     vmem_create(const char *name, vmem_addr_t base, vmem_size_t size,
         vmem_size_t quantum,
         int (*allocfn)(void *, vmem_size_t, vmem_size_t *, vm_flag_t, vmem_addr_t *),
         void (*freefn)(void *, vmem_addr_t, vmem_size_t), void *arg,
         vmem_size_t qcache_max, vm_flag_t flags, int ipl);

     int
     vmem_add(vmem_t *vm, vmem_addr_t addr, vmem_size_t size, vm_flag_t flags,
         vmem_addr_t *addrp);

     int
     vmem_xalloc(vmem_t *vm, vmem_size_t size, vmem_size_t align,
         vmem_size_t phase, vmem_size_t nocross, vmem_addr_t minaddr,
         vmem_addr_t maxaddr, vm_flag_t flags, vmem_addr_t *addrp);

     void
     vmem_xfree(vmem_t *vm, vmem_addr_t addr, vmem_size_t size);

     int
     vmem_alloc(vmem_t *vm, vmem_size_t size, vm_flag_t flags,
         vmem_addr_t *addrp);

     void
     vmem_free(vmem_t *vm, vmem_addr_t addr, vmem_size_t size);

     void
     vmem_destroy(vmem_t *vm);

DESCRIPTION
     The vmem is a general purpose resource allocator.  Despite its name, it
     can be used for arbitrary resources other than virtual memory.

     vmem_create() creates a new vmem arena.

     name        The string to describe the vmem.

     base        The start address of the initial span.  Pass 0 if no initial
                 span is required.

     size        The size of the initial span.  Pass 0 if no initial span is
                 required.

     quantum     The smallest unit of allocation.

     allocfn     The callback function used to import spans from the backend
                 arena.  Set both allocfn and freefn to NULL to disable auto-
                 matic imports.  vmem calls (*allocfn)(arg, size, &actualsize,
                 flags, &addrp) to import a span of size at least size.
                 allocfn should accept the same flags as vmem_alloc().
                 allocfn must return ENOMEM to indicate failure, or 0 on suc-
                 cess.  If allocfn succeeds, it must write the actual size of
                 the allocation to actualsize and the starting address of the
                 imported span to addrp.  The actual size will always be
                 greater than or equal to the requested size.

     freefn      The callback function used to free spans to the backend
                 arena.  freefn may be NULL even if allocfn is not NULL.  vmem
                 calls (*freefn)(arg, addr, size) to return to arg a span of
                 size size, starting at addr, that was previously allocated by
                 allocfn.

     arg         The backend arena.  arg may be NULL.  vmem passes arg as the
                 first argument of allocfn and freefn.

     qcache_max  The largest size of allocations which can be served by quan-
                 tum cache.  It is merely a hint and can be ignored.

     flags       Either of:

                 VM_SLEEP    Can sleep until enough resources are available.

                 VM_NOSLEEP  Don't sleep.  Immediately return NULL if there
                             are not enough resources available.

     ipl         Interrupt level to be blocked for allocating from vmem.

     vmem_add() adds a span of size size starting at addr to the arena.
     Returns 0 on success, ENOMEM on failure.  flags should be one of:

     VM_SLEEP    Can sleep until enough resources are available.

     VM_NOSLEEP  Don't sleep.  Immediately return ENOMEM if there are not
                 enough resources available.

     vmem_xalloc() allocates a resource from the arena.

     vm       The arena which we allocate from.

     size     Specify the size of the allocation.

     align    If zero, don't care about the alignment of the allocation.  Oth-
              erwise, request a resource segment starting at offset phase from
              an align aligned boundary.

     phase    See the above description of align.  If align is zero, phase
              should be zero.  Otherwise, phase should be smaller than align.

     nocross  Request a resource which doesn't cross nocross aligned boundary.

     minaddr  Specify the minimum address which can be allocated, or
              VMEM_ADDR_MIN if the caller does not care.

     maxaddr  Specify the maximum address which can be allocated, or
              VMEM_ADDR_MAX if the caller does not care.

     flags    A bitwise OR of an allocation strategy and a sleep flag.

              The allocation strategy is one of:

              VM_BESTFIT     Prefer space efficiency.

              VM_INSTANTFIT  Prefer performance.

              The sleep flag should be one of:

              VM_SLEEP    Can sleep until enough resources are available.

              VM_NOSLEEP  Don't sleep.  Immediately return ENOMEM if there are
                          not enough resources available.

     addrp    On success, if addrp is not NULL, vmem_xalloc() overwrites it
              with the start address of the allocated span.

     vmem_xfree() frees resource allocated by vmem_xalloc() to the arena.

     vm    The arena which we free to.

     addr  The resource being freed.  It must be the one returned by
           vmem_xalloc().  Notably, it must not be the one from vmem_alloc().
           Otherwise, the behaviour is undefined.

     size  The size of the resource being freed.  It must be the same as the
           size argument used for vmem_xalloc().

     vmem_alloc() allocates a resource from the arena.

     vm     The arena which we allocate from.

     size   Specify the size of the allocation.

     flags  A bitwise OR of an allocation strategy and a sleep flag.

            The allocation strategy is one of:

            VM_BESTFIT     Prefer space efficiency.

            VM_INSTANTFIT  Prefer performance.

            The sleep flag should be one of:

            VM_SLEEP    Can sleep until enough resources are available.

            VM_NOSLEEP  Don't sleep.  Immediately return ENOMEM if there are
                        not enough resources available.

     addrp  On success, if addrp is not NULL, vmem_alloc() overwrites it with
            the start address of the allocated span.

     vmem_free() frees resource allocated by vmem_alloc() to the arena.

     vm    The arena which we free to.

     addr  The resource being freed.  It must be the one returned by
           vmem_alloc().  Notably, it must not be the one from vmem_xalloc().
           Otherwise, the behaviour is undefined.

     size  The size of the resource being freed.  It must be the same as the
           size argument used for vmem_alloc().

     vmem_destroy() destroys a vmem arena.

     vm  The vmem arena being destroyed.  The caller should ensure that no one
         will use it anymore.

RETURN VALUES
     vmem_create() return a pointer to the newly allocated vmem_t.  Otherwise,
     it returns NULL.

     On success, vmem_xalloc() and vmem_alloc() return 0.  Otherwise, ENOMEM
     is returned.

CODE REFERENCES
     The vmem subsystem is implemented within the file sys/kern/subr_vmem.c.

SEE ALSO
     intro(9), kmem(9), memoryallocators(9), uvm(9)

     Jeff Bonwick and Jonathan Adams, "Magazines and Vmem: Extending the Slab
     Allocator to Many CPUs and Arbitrary Resources", 2001 USENIX Annual
     Technical Conference, 2001.

AUTHORS
     This implementation of vmem was written by YAMAMOTO Takashi.

BUGS
     vmem relies on malloc(9), pool(9), and RUN_ONCE(9), so it cannot be used
     as early during system bootstrap as extent(9).

NetBSD 6.0                     September 2, 2011                    NetBSD 6.0

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