On Sat, 14 Jun 2008 10:51:19 +0800
"Peter Teoh" <htmldeveloper@xxxxxxxxx> wrote:
> first, it should attempt to allocate space from physical mem...and it
> uses max_pfn as the mark to guide it.
No.
> On the other hand, because i cannot find the link between max_pfn and
> __get_free_pages() - so question is how does __get_free_pages() know
> where the max pfn it can used for memory allocation?
You read correctly, __get_free_pages() has absolutely nothing to
do with max_pfn.
> next, it should then update the pagetable entries - right?\
No, __get_free_pages() never manipulates page tables.
> essentially...it should be marking the pagetable entries for the block
> of memory as "notfree" - right? what is the function used? thanks.
This info is not kept in page tables, but in the array
struct page mem_map[].
Take a look at the functions that __get_free_pages() calls:
alloc_pages()
-> alloc_pages_node()
-> __alloc_pages()
-> __alloc_pages_internal()
-> get_page_from_freelist()
-> buffered_rmqueue()
-> rmqueue_bulk()
-> __rmqueue()
-> __rmqueue_smallest()
As you can see, each zone has a number of free lists, for each
allocation order:
/* Find a page of the appropriate size in the preferred list */
for (current_order = order; current_order < MAX_ORDER; ++current_order) {
area = &(zone->free_area[current_order]);
if (list_empty(&area->free_list[migratetype]))
continue;
page = list_entry(area->free_list[migratetype].next,
struct page, lru);
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