Linux Virtual Memory Subsystem
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
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