Question

I found alloc_pages() is called by alloc_fresh_huge_page_node() to allocate one huge page, just want to confirm if it allocates one physical huge page and also builds memory mapping?

static struct page *alloc_fresh_huge_page_node(struct hstate *h, int nid)
{
    struct page *page;

    if (h->order >= MAX_ORDER)
        return NULL;

    page = alloc_pages_exact_node(nid,
        htlb_alloc_mask|__GFP_COMP|__GFP_THISNODE|
                        __GFP_REPEAT|__GFP_NOWARN,
            huge_page_order(h));
    if (page) {
        if (arch_prepare_hugepage(page)) {
            __free_pages(page, huge_page_order(h));
            return NULL;
        }
        prep_new_huge_page(h, page, nid);
    }

    return page;
}

Answer 1

Alloc_pages() allocates whichever possible page size you use it for. 2MB is one option (typically when using PAE), the others being, on the 2.6 kernel, 4kb and 4MB.