由vmalloc()分配的内存线性地址空间在VMALLOC_START之上，并且其分配的物理内存也是在896M之上的高端内存中的。
/**
* vmalloc - allocate virtually contiguous memory
* @size: allocation size
* Allocate enough pages to cover @size from the page level
* allocator and map them into contiguous kernel virtual space.
*
* For tight control over page level allocator and protection flags
* use __vmalloc() instead.
*/
void *vmalloc(unsigned long size)
{
//注意__GFP_HIGHMEM这个flag
return __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM,
PAGE_KERNEL);
}
static inline struct page *alloc_pages_node(int nid, gfp_t gfp_mask,
unsigned int order)
{
if (unlikely(order >= MAX_ORDER))
return NULL;
/* Unknown node is current node */
if (nid < 0)
nid = numa_node_id();
//最后调用的参数是zode_zonelists+ZONE_HIGHMEM，即是优先考虑高端内存区
return __alloc_pages(gfp_mask, order,
NODE_DATA(nid)->node_zonelists + gfp_zone(gfp_mask));
}
static inline enum zone_type gfp_zone(gfp_t flags)
{
#ifdef CONFIG_ZONE_DMA
if (flags & __GFP_DMA)
return ZONE_DMA;
#endif
#ifdef CONFIG_ZONE_DMA32
if (flags & __GFP_DMA32)
return ZONE_DMA32;
#endif
#ifdef CONFIG_HIGHMEM
if (flags & __GFP_HIGHMEM) //高端内存
return ZONE_HIGHMEM;
#endif
return ZONE_NORMAL;
}
/*
* This is the 'heart' of the zoned buddy allocator.
*/
struct page * fastcall
__alloc_pages(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist)
{
const gfp_t wait = gfp_mask & __GFP_WAIT;
struct zone **z;
struct page *page;
struct reclaim_state reclaim_state;
struct task_struct *p = current;
int do_retry;
int alloc_flags;
int did_some_progress;
might_sleep_if(wait);
if (should_fail_alloc_page(gfp_mask, order))
return NULL;
restart:
z = zonelist->zones; /* the list of zones suitable for gfp_mask */
if (unlikely(*z == NULL)) {
/* Should this ever happen?? */
return NULL;
}
page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order,
zonelist, ALLOC_WMARK_LOW|ALLOC_CPUSET);
if (page)
goto got_pg;
......
}