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KM_ALLOC(9) FreeBSD Kernel Developer's Manual KM_ALLOC(9) NAME km_alloc, km_free - kernel memory allocator SYNOPSIS #include <sys/types.h> #include <uvm/uvm_extern.h> void * km_alloc(size_t sz, const struct kmem_va_mode *kv, const struct kmem_pa_mode *kp, const struct kmem_dyn_mode *kd); void km_free(void *v, size_t sz, const struct kmem_va_mode *kv, const struct kmem_pa_mode *kp); DESCRIPTION The km_alloc() function allocates kernel virtual space optionally backed by physical pages. The km_free() function frees the space that was previously allocated by km_alloc(). The sz argument specifies the size of the allocation and must be a multiple of PAGE_SIZE. The kv and kp arguments specify the type of virtual and physical memory to be allocated. The kd argument specifies additional options for the allocation. The arguments passed to km_free() must match those that were used to obtain the space in km_alloc(). Typically a user will use certain predefined modes for memory allocation. For virtual space the predefined modes are: kv_any Allocates the virtual space anywhere. kv_intrsafe Allocates the virtual space in the interrupt safe map. kv_page Allocates single pages. For physical pages the predefined modes are: kp_dirty Maps dirty pages into the allocation. kp_zero Maps zeroed pages into the allocation. kp_dma Maps dma-accessible pages into the allocation. kp_dma_zero Maps zeroed dma-accessible pages into the allocation. kp_pageable Pages will be demand paged. kp_none Leaves the allocation unmapped. The other parameters for allocation are: kd_waitok Sleeping for physical pages is allowed. kd_nowait Sleeping is not allowed. kd_trylock Fail if the allocator cannot obtain locks without waiting. In case the predefined allocation modes are not sufficient, a custom allocation mode can be created. The structure controlling the virtual space allocation is: struct kmem_va_mode { struct vm_map **kv_map; vsize_t kv_align; int kv_wait; int kv_singlepage; }; kv_map A pointer to the pointer to the uvm_map the space will be allocated from. kv_align Alignment constraint of the allocated space. kv_wait A flag indicating whether the allocator should wait for space to be freed if the allocation cannot be satisfied. kv_singlepage A flag indicating if the allocations will always be for single pages. struct kmem_pa_mode { struct uvm_constraint_range *kp_constraint; struct uvm_object **kp_object; paddr_t kp_align; paddr_t kp_boundary; int kp_nomem; int kp_maxseg; int kp_zero; int kp_pageable; }; kp_constraint A pointer to physical allocation constraints. kp_object A pointer to a pointer to a uvm_object if the pages should be backed by a kernel object. kp_align Physical alignment of the first page in the allocation. kp_boundary Boundary that the physical addresses can't cross if the allocation is contiguous. kp_nomem A flag that specifies that the allocation should not be backed by physical pages. kp_maxseg Maximal amount of contiguous physical segments in the allocation. kp_zero A flag that specifies if the returned memory should be zeroed. kp_pageable A flag that specifies if the returned memory should be demand paged from the backing object instead of being allocated up front. struct kmem_dyn_mode { int kd_waitok; int kd_trylock; voff_t kd_prefer; int *kd_slowdown; }; kd_waitok A flag that specifies if the allocator may sleep waiting for memory. kd_trylock A flag that specifies if the allocator should fail if it can't immediately obtain a lock. kd_prefer An offset given to PMAP_PREFER to virtually align the allocated space. kd_slowdown A pointer to an integer that will be set to 1 if the internal single page allocator needs the caller to back off to allow the allocator to catch up. RETURN VALUES km_alloc() returns a kernel virtual address or NULL if the allocation cannot be satisfied. SEE ALSO malloc(9), uvm_init(9) FreeBSD 14.1-RELEASE-p8 December 6, 2019 FreeBSD 14.1-RELEASE-p8