UVM_PAGEALLOC(9) | Kernel Developer's Manual | UVM_PAGEALLOC(9)

# NAME

`uvm_pagealloc`, `uvm_pagerealloc`, `uvm_pagefree`, `uvm_pglistalloc`, `uvm_pglistfree`, `uvm_page_physload` — physical memory allocator

# SYNOPSIS

`#include <sys/param.h>`
`#include <uvm/uvm.h>`

struct vm_page *
`uvm_pagealloc`(struct uvm_object *uobj, voff_t off, struct vm_anon *anon, int flags);

void
`uvm_pagerealloc`(struct vm_page *pg, struct uvm_object *newobj, voff_t newoff);

void
`uvm_pagefree`(struct vm_page *pg);

int
`uvm_pglistalloc`(psize_t size, paddr_t low, paddr_t high, paddr_t alignment, paddr_t boundary, struct pglist *rlist, int nsegs, int flags);

void
`uvm_pglistfree`(struct pglist *list);

void
`uvm_page_physload`(paddr_t start, paddr_t end, paddr_t avail_start, paddr_t avail_end, int free_list);

# DESCRIPTION

The `uvm_pagealloc`() function allocates a page of memory at virtual address off in either the object uobj or the anonymous memory anon, or returns `NULL` if no pages are free. Only one of anon and uobj can be non `NULL`. The flags can be any of:

    #define UVM_PGA_USERESERVE      0x0001  /* ok to use reserve pages */
    #define UVM_PGA_ZERO            0x0002  /* returned page must be zeroed */

The `UVM_PGA_USERESERVE` flag means to allocate a page even if that will result in the number of free pages being lower than `uvmexp.reserve_pagedaemon` (if the current thread is the pagedaemon) or `uvmexp.reserve_kernel` (if the current thread is not the pagedaemon). The `UVM_PGA_ZERO` flag causes the returned page to be filled with zeroes, either by allocating it from a pool of pre-zeroed pages or by zeroing it in-line as necessary.

The `uvm_pagerealloc`() function reallocates page pg to a new object newobj, at a new offset newoff.

The `uvm_pagefree`() function frees the physical page pg.

The `uvm_pglistalloc`() function allocates a list of pages for size size byte under various constraints. low and high describe the lowest and highest addresses acceptable for the list. If alignment is non-zero, it describes the required alignment of the list, in power-of-two notation. If boundary is non-zero, no segment of the list may cross this power-of-two boundary, relative to zero. nsegs is the maximum number of physically contiguous segments. The allocated memory is returned in the rlist list. The flags can be any of:

    #define UVM_PLA_WAITOK	0x0001	/* may sleep */
    #define UVM_PLA_NOWAIT	0x0002	/* can't sleep */
    #define UVM_PLA_ZERO	0x0004	/* zero all pages before returning */

The `UVM_PLA_WAITOK` flag means that the function may sleep while trying to allocate the list of pages (this is currently ignored). Conversely, the `UVM_PLA_NOWAIT` flag signifies that the function may not sleep while allocating. It is an error not to provide one of the above flags. Optionally, one may also specify the `UVM_PLA_ZERO` flag to receive zeroed memory in the page list.

The `uvm_pglistfree`() function frees the list of pages pointed to by list.

The `uvm_page_physload`() function loads physical memory segments into VM space on the specified free_list. `uvm_page_physload`() must be called at system boot time to set up physical memory management pages. The arguments describe the start and end of the physical addresses of the segment, and the available start and end addresses of pages not already in use.

August 24, 2024 | Debian