Allocating Kernel Memory

There are several different methods of allocating kernel memory at runtime.

• The bootmem allocator is used to reserve pages for static kernel data during the early boot process.

• alloc_pages() is the basic interface to the zone allocator, which hands you a page struct representing a (range of) physical pages.

• get_free_pages() is a slightly nicer interface to alloc_pages() which returns the virtual address in kernel memory, rather than a page struct pointer. get_free_pages() only works for low memory. [This is not enforced, but it looks like if you call get_free_pages() with GFP_HIGHMEM, Bad Things can happen.]

• kmalloc() is the slab allocator, which uses the zone allocator to whack off chunks of kernel physically-mapped-virtual pages, and carves them up into smaller bits for particular uses.

• vmalloc() allocates arbitrary physical pages and maps them into kernel VM contiguously.

• kmap() temporarily maps *any* physical page into kernel VM.

Physical MM	Linux MM Outline	The Page Cache

Questions and comments to Joe Knapka

The LXR links in this page were produced by lxrreplace.tcl, which is available for free.

Credits