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CONTIGMALLOC(9)       DragonFly Kernel Developer's Manual      CONTIGMALLOC(9)


NAME

     contigmalloc, contigfree -- manage contiguous kernel physical memory


SYNOPSIS

     #include <sys/types.h>
     #include <sys/malloc.h>

     void *
     contigmalloc(unsigned long size, struct malloc_type *type, int flags,
         vm_paddr_t low, vm_paddr_t high, unsigned long alignment,
         unsigned long boundary);

     void
     contigfree(void *addr, unsigned long size, struct malloc_type *type);


DESCRIPTION

     The contigmalloc() function allocates size bytes of contiguous physical
     memory that is aligned to alignment bytes, and which does not cross a
     boundary of boundary bytes.  If successful, the allocation will reside
     between physical addresses low and high.  The returned pointer points to
     a wired kernel virtual address range of size bytes allocated from the
     kernel virtual address (KVA) map.  The type argument is ignored.

     The flags parameter modifies contigmalloc()'s behavior as follows:

           M_WAITOK  Causes contigmalloc() to try flushing the active page
                     queue in its second pass.  Note that (unlike
                     kmalloc(M_WAITOK)) contigmalloc(M_WAITOK) can still
                     return NULL.

           M_ZERO    Causes the allocated physical memory to be zero filled.

     Other flags (if present) are ignored.

     The contigfree() function deallocates memory allocated by a previous call
     to contigmalloc().


IMPLEMENTATION NOTES

     The contigmalloc() function does not sleep waiting for memory resources
     to be freed up, but instead scans available physical memory a small num-
     ber of times for a suitably sized free address range before giving up.
     Memory allocation is done on a first-fit basis, starting from the top of
     the provided address range.


RETURN VALUES

     The contigmalloc() function returns a kernel virtual address if alloca-
     tion succeeds, or NULL otherwise.


EXAMPLES

     void *p;
     p = contigmalloc(8192, M_DEVBUF, M_ZERO, 0, (1L << 22),
         32 * 1024, 1024 * 1024);

     Ask for 8192 bytes of zero-filled memory residing between physical
     address 0 and 4194303 inclusive, aligned to a 32K boundary and not cross-
     ing a 1M address boundary.


DIAGNOSTICS

     The contigmalloc() function will panic if size is zero, or if alignment
     or boundary is not a power of two.


SEE ALSO

     kmalloc(9)

DragonFly 3.5                  January 19, 2008                  DragonFly 3.5

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