Linux Kernel Architecture

Chapter3:MemoryManagement

mm/vmalloc.c

void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,

pgprot_t prot, int node)

{

...

for (i = 0; i < area->nr_pages; i++) {

if (node < 0)

area->pages[i] = alloc_page(gfp_mask);

else

area->pages[i] = alloc_pages_node(node, gfp_mask, 0);

}

...

if (map_vm_area(area, prot, &pages))

goto fail;

return area->addr;

...

}

Return address

Allocate as manypages as necessary

Allocate memory for

page instances

vmalloc

_vmalloc_node

get_vm_area_node

alloc_pages_node

_vmalloc_area_node

_vmalloc

Figure 3-39: Code flow diagram forvmalloc.

If an explicit node is specified from which the pages are to be allocated, the kernel invokes
alloc_pages_node. Otherwise, pages are taken from the current node usingalloc_page.

The pages are removed from the buddy systemof the relevant node; when this is done,vmallocsets
gfp_masktoGFP_KERNEL | __GFP_HIGHMEM— the kernel instructs memory management to take the pages
fromZONE_HIGHMEMif possible. The reasons for this were given above: Pages from the lower-memory
areas are more valuable and should therefore not be wasted forvmallocallocations that could just as
well be satisfied with high-memory pages.

Memory is taken from the buddy system, andgfp_maskis set toGFP_KERNEL | __GFP_HIGHMEMso that the
kernel instructs memory management to take the pages fromZONE_HIGHMEMif possible. We have already
seen the reasons.