contigmalloc(9) contigfree


In sys/types.h In sys/malloc.h Ft void * Fo contigmalloc Fa unsigned long size Fa struct malloc_type *type Fa int flags Fa vm_paddr_t low Fa vm_paddr_t high Fa unsigned long alignment Fa vm_paddr_t boundary Fc Ft void Fo contigfree Fa void *addr Fa unsigned long size Fa struct malloc_type *type Fc


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

The Fa flags parameter modifies Fn contigmalloc Ns 's behaviour as follows:

Causes the allocated physical memory to be zero filled.
Causes Fn contigmalloc to return NULL if the request cannot be immediately fulfilled due to resource shortage.

Other flags (if present) are ignored.

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


The Fn contigmalloc function does not sleep waiting for memory resources to be freed up, but instead actively reclaims pages before giving up. However, unless M_NOWAIT is specified, it may select a page for reclamation that must first be written to backing storage, causing it to sleep.


The Fn contigmalloc function returns a kernel virtual address if allocation succeeds, or NULL otherwise.


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 crossing a 1M address boundary.


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