[PATCH 3/6] struct page: add field for vm_struct

[Igor Stoppa]

When a page is used for virtual memory, it is often necessary to obtian
a handler to the corresponding vm_struct, which refers to the virtually
continuous area generated when invoking vmalloc.

The struct page has a "mapping" field, which can be re-used, to store a
pointer to the parent area. This will avoid more expensive searches.

As example, the function find_vm_area is reimplemented, to take advantage
of the newly introduced field.

Signed-off-by: Igor Stoppa <igor.sto...@huawei.com>
---
 include/linux/mm_types.h |  1 +
 mm/vmalloc.c             | 18 +++++++++++++-----
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index fd1af6b9591d..c3a4825e10c0 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -84,6 +84,7 @@ struct page {
                void *s_mem;                    /* slab first object */
                atomic_t compound_mapcount;     /* first tail page */
                /* page_deferred_list().next     -- second tail page */
+               struct vm_struct *area;
        };
 
        /* Second double word */
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 673942094328..9404ffd0ee98 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1466,13 +1466,16 @@ struct vm_struct *get_vm_area_caller(unsigned long 
size, unsigned long flags,
  */
 struct vm_struct *find_vm_area(const void *addr)
 {
-       struct vmap_area *va;
+       struct page *page;
 
-       va = find_vmap_area((unsigned long)addr);
-       if (va && va->flags & VM_VM_AREA)
-               return va->vm;
+       if (unlikely(!is_vmalloc_addr(addr)))
+               return NULL;
 
-       return NULL;
+       page = vmalloc_to_page(addr);
+       if (unlikely(!page))
+               return NULL;
+
+       return page->area;
 }
 
 /**
@@ -1536,6 +1539,7 @@ static void __vunmap(const void *addr, int 
deallocate_pages)
                        struct page *page = area->pages[i];
 
                        BUG_ON(!page);
+                       page->area = NULL;
                        __free_pages(page, 0);
                }
 
@@ -1744,6 +1748,7 @@ void *__vmalloc_node_range(unsigned long size, unsigned 
long align,
                        const void *caller)
 {
        struct vm_struct *area;
+       unsigned int i;
        void *addr;
        unsigned long real_size = size;
 
@@ -1769,6 +1774,9 @@ void *__vmalloc_node_range(unsigned long size, unsigned 
long align,
 
        kmemleak_vmalloc(area, size, gfp_mask);
 
+       for (i = 0; i < area->nr_pages; i++)
+               area->pages[i]->area = area;
+
        return addr;
 
 fail:
-- 
2.14.1