Virtual Memory

Linux process virtual memory layout

Expand of user stack

vmalloc

vm_struct

• From vm_start to vm_end
• User space page table saved in here
• Each process is not identical
• vmalloc is often slower than kmalloc, because it may have to remap the buffer space into a virtually contiguous range
• Most of the time we use kmalloc

slab/slub alloc

kmalloc()

• The requirements is similar with user space heap
• Kernel alloc small size memory.
• Difference with kernel stack
• task_struct storage here?
• Heavy use cache.
• kmalloc is limited in the size of buffer it can provide: 128 KBytes(4MB in 2.6.33)
• physically contiguous
• Can specific the zone to alloc memory. (Normal, High, DMA)

buddy alloc

• Physical page management.