NAME

       vmem — general purpose resource 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,
           vmem_size_t qcache_max, int flags);

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

       int
       vmem_xalloc(vmem_t  *vm,  const  vmem_size_t  size,   vmem_size_t   align,   const   vmem_size_t   phase,
           const  vmem_size_t  nocross,  const  vmem_addr_t  minaddr,  const  vmem_addr_t  maxaddr,  int  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, int 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.

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

       flags       malloc(9) wait flag.

       vmem_add() adds a span of size size starting at addr to the arena.   Returns  0  on  success,  ENOMEM  on
       failure.  flags is malloc(9) wait flag.

       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.  Otherwise, 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 malloc(9) wait flag.  The allocation strategy is
                one of:

                M_FIRSTFIT
                        Prefer allocation performance.

                M_BESTFIT
                        Prefer space efficiency.

                M_NEXTFIT
                        Perform an address-ordered search for  free  addresses,  beginning  where  the  previous
                        search ended.

       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 vmem allocation strategy flag (see above) and a malloc(9) sleep flag.

       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() returns 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

       malloc(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.

HISTORY

       The vmem allocator was originally implemented in NetBSD.  It was introduced in FreeBSD 10.0.

AUTHORS

       Original implementation of vmem was written by YAMAMOTO Takashi.  The  FreeBSD  port  was  made  by  Jeff
       Roberson.

BUGS

       vmem relies on malloc(9), so it cannot be used as early during system bootstrap.

Debian                                            May 17, 2019                                           VMEM(9)