CONTIGMALLOC(9FREEBSD) - man page online | system kernel interfaces

Manage contiguous kernel physical memory.

July 19, 2007
CONTIGMALLOC(9)                   BSD Kernel Developer's Manual                   CONTIGMALLOC(9)


contigmalloc, contigfree — manage contiguous kernel physical memory


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


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 suc‐ cessful, 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 ker‐ nel virtual address (KVA) map. The flags parameter modifies contigmalloc()'s behaviour as follows: M_ZERO Causes the allocated physical memory to be zero filled. M_NOWAIT Causes contigmalloc() to return NULL if the request cannot be immediately fulfilled due to resource shortage. Other flags (if present) are ignored. The contigfree() function deallocates memory allocated by a previous call to contigmalloc().


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


malloc(9), memguard(9)
BSD July 19, 2007 BSD
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contigmalloc(9freebsd) referred by contigfree(9freebsd) | free(9freebsd) | malloc(9freebsd) | MALLOC_DECLARE(9freebsd) | MALLOC_DEFINE(9freebsd) | memguard(9freebsd) | realloc(9freebsd) | reallocf(9freebsd)
refer to malloc(9freebsd) | memguard(9freebsd)