Kernel 3.0.8 内存管理函数
1. 内存分配函数
相关代码如下：
#define alloc_pages(gfp_mask, order) alloc_pages_node(numa_node_id(), gfp_mask, order)
#define alloc_page_vma(gfp_mask, vma, addr) alloc_pages(gfp_mask, 0)
#define alloc_page(gfp_mask) alloc_pages(gfp_mask, 0)
#define __get_free_page(gfp_mask) __get_free_pages((gfp_mask),0)
#define __get_dma_pages(gfp_mask, order) __get_free_pages((gfp_mask) | GFP_DMA,(order))
#define pfn_to_page(pfn) (mem_map + ((pfn) - PHYS_PFN_OFFSET))
#define page_to_pfn(page) ((unsigned long)((page) - mem_map) + PHYS_PFN_OFFSET)
#define pfn_valid(pfn) ((pfn) >= PHYS_PFN_OFFSET && (pfn) < (PHYS_PFN_OFFSET + max_mapnr))
#define phys_to_page(phys) (pfn_to_page(phys >> PAGE_SHIFT))
#define page_to_phys(page) (page_to_pfn(page) << PAGE_SHIFT)
#define virt_to_page(kaddr) pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
#define virt_addr_valid(kaddr) pfn_valid(__pa(kaddr) >> PAGE_SHIFT)
1）__get_free_pages实现代码如下，它返回页的虚拟地址：
unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order)
{
struct page *page;
/*
* __get_free_pages() returns a 32-bit address, which cannot represent
* a highmem page
*/
VM_BUG_ON((gfp_mask & __GFP_HIGHMEM) != 0);
page = alloc_pages(gfp_mask, order);
if (!page)
return 0;
return (unsigned long) page_address(page);
}
/**
* page_address - get the mapped virtual address of a page
* @page: &struct page to get the virtual address of
*
* Returns the page's virtual address.
*/
void *page_address(struct page *page)
{
unsigned long flags;
void *ret;
struct page_address_slot *pas;
if (!PageHighMem(page))
return lowmem_page_address(page);
pas = page_slot(page);
ret = NULL;
spin_lock_irqsave(&pas->lock, flags);
if (!list_empty(&pas->lh)) {
struct page_address_map *pam;
list_for_each_entry(pam, &pas->lh, list) {
if (pam->page == page) {
ret = pam->virtual;
goto done;
}
}
}
done:
spin_unlock_irqrestore(&pas->lock, flags);
return ret;
}
static __always_inline void *lowmem_page_address(struct page *page)
{
return __va(PFN_PHYS(page_to_pfn(page)));
}
2）alloc_pages_node
static inline struct page *alloc_pages_node(int nid, gfp_t gfp_mask,
unsigned int order)
{
/* Unknown node is current node */
if (nid < 0)
nid = numa_node_id();
return __alloc_pages(gfp_mask, order, node_zonelist(nid, gfp_mask));
}
参数nid是要分配内存的 NUMA节点 ID，
参数gfp_mask是 GFP_分配标志,
参数order是分配内存的大小(2^order个页面).
返回值是一个指向第一个(可能返回多个页)page结构的指针,失败时返回NULL。
static inline struct page *
__alloc_pages(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist)
{
return __alloc_pages_nodemask(gfp_mask, order, zonelist, NULL);
}
/*
* This is the 'heart' of the zoned buddy allocator.
*/
struct page *
__alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist, nodemask_t *nodemask)
{
enum zone_type high_zoneidx = gfp_zone(gfp_mask);
struct zone *preferred_zone;
struct page *page;
int migratetype = allocflags_to_migratetype(gfp_mask);
gfp_mask &= gfp_allowed_mask;
lockdep_trace_alloc(gfp_mask);
might_sleep_if(gfp_mask & __GFP_WAIT);
if (should_fail_alloc_page(gfp_mask, order))
return NULL;
/*
* Check the zones suitable for the gfp_mask contain at least one
* valid zone. It's possible to have an empty zonelist as a result
* of GFP_THISNODE and a memoryless node
*/
if (unlikely(!zonelist->_zonerefs->zone))
return NULL;
get_mems_allowed();
/* The preferred zone is used for statistics later */
first_zones_zonelist(zonelist, high_zoneidx,
nodemask ? : &cpuset_current_mems_allowed,
&preferred_zone);
if (!preferred_zone) {
put_mems_allowed();
return NULL;
}
/* First allocation attempt */
page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order,
zonelist, high_zoneidx, ALLOC_WMARK_LOW|ALLOC_CPUSET,
preferred_zone, migratetype);
if (unlikely(!page))
page = __alloc_pages_slowpath(gfp_mask, order,
zonelist, high_zoneidx, nodemask,
preferred_zone, migratetype);
put_mems_allowed();
trace_mm_page_alloc(page, order, gfp_mask, migratetype);
return page;
}
其接下来的主要调用流程如下：
get_page_from_freelist->
buffered_rmqueue
3) buffered_rmqueue
从区域zone中获取一块大小为2^order的物理内存块，返回该内存块的首个页框的描述符page。
static inline
struct page *buffered_rmqueue(struct zone *preferred_zone,
struct zone *zone, int order, gfp_t gfp_flags,
int migratetype)
{
unsigned long flags;
struct page *page;
int cold = !!(gfp_flags & __GFP_COLD);
again:
if (likely(order == 0)) { //获取一页物理内存(2^0),从当前cpu的高速缓存内存中申请
struct per_cpu_pages *pcp;
struct list_head *list;
local_irq_save(flags);
pcp = &this_cpu_ptr(zone->pageset)->pcp; //获取zone的当前处理器的高速缓存内存描述结构指针
list = &pcp->lists[migratetype];
if (list_empty(list)) { //高速缓存内存为空
pcp->count += rmqueue_bulk(zone, 0,//调用此函数从伙伴系统中分配batch空闲内存到高速缓存内存中
pcp->batch, list,
migratetype, cold);
if (unlikely(list_empty(list)))
goto failed;
}
//我们从pcp->list链表开始的第一个lru起，去寻找相应的struct page结构体
if (cold)
page = list_entry(list->prev, struct page, lru);
else
page = list_entry(list->next, struct page, lru);
//由于被分配出去了，所以高速缓存内存中不再包含这页内存，所以从链表里删除这一项。
list_del(&page->lru);
pcp->count--; //相应的当前页数也要减少
} else { //获取一块物理内存(2^order)
if (unlikely(gfp_flags & __GFP_NOFAIL)) {
/*
* __GFP_NOFAIL is not to be used in new code.
*
* All __GFP_NOFAIL callers should be fixed so that they
* properly detect and handle allocation failures.
*
* We most definitely don't want callers attempting to
* allocate greater than order-1 page units with
* __GFP_NOFAIL.
*/
WARN_ON_ONCE(order > 1);
}
spin_lock_irqsave(&zone->lock, flags);
page = __rmqueue(zone, order, migratetype); //调用函数申请内存
spin_unlock(&zone->lock);
if (!page)
goto failed;
__mod_zone_page_state(zone, NR_FREE_PAGES, -(1 << order));
}
__count_zone_vm_events(PGALLOC, zone, 1 << order);
zone_statistics(preferred_zone, zone, gfp_flags);
local_irq_restore(flags);
VM_BUG_ON(bad_range(zone, page));
if (prep_new_page(page, order, gfp_flags))
goto again;
return page; //返回申请到的内存空间的首页内存页的struct page结构指针
failed:
local_irq_restore(flags);
return NULL;
}
4) rmqueue_bulk
用于多次（count）内存申请.
/*
* Obtain a specified number of elements from the buddy allocator, all under
* a single hold of the lock, for efficiency. Add them to the supplied list.
* Returns the number of new pages which were placed at *list.
*/
static int rmqueue_bulk(struct zone *zone, unsigned int order,
unsigned long count, struct list_head *list,
int migratetype, int cold)
{
int i;
spin_lock(&zone->lock);
for (i = 0; i < count; ++i) {
struct page *page = __rmqueue(zone, order, migratetype);
if (unlikely(page == NULL))
break;
/*
* Split buddy pages returned by expand() are received here
* in physical page order. The page is added to the callers and
* list and the list head then moves forward. From the callers
* perspective, the linked list is ordered by page number in
* some conditions. This is useful for IO devices that can
* merge IO requests if the physical pages are ordered
* properly.
*/
if (likely(cold == 0))
list_add(&page->lru, list);
else
list_add_tail(&page->lru, list);
set_page_private(page, migratetype);
list = &page->lru;
}
__mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order));
spin_unlock(&zone->lock);
return i;
}
5) __rmqueue
用于一次内存申请。
/*
* Do the hard work of removing an element from the buddy allocator.
* Call me with the zone->lock already held.
*/
static struct page *__rmqueue(struct zone *zone, unsigned int order,
int migratetype)
{
struct page *page;
retry_reserve:
page = __rmqueue_smallest(zone, order, migratetype);
if (unlikely(!page) && migratetype != MIGRATE_RESERVE) {
page = __rmqueue_fallback(zone, order, migratetype);
/*
* Use MIGRATE_RESERVE rather than fail an allocation. goto
* is used because __rmqueue_smallest is an inline function
* and we want just one call site
*/
if (!page) {
migratetype = MIGRATE_RESERVE;
goto retry_reserve;
}
}
trace_mm_page_alloc_zone_locked(page, order, migratetype);
return page;
}
2. 内存释放函数
相关宏定义如下：
#define __free_page(page) __free_pages((page), 0) #define free_page(addr) free_pages((addr),0)