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man page of contigmalloc

contigmalloc: manage contiguous kernel physical memory

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, unsigned long 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 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 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) CONTIGMALLOC(9)

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