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Subject[PATCH 3/6] struct page: add field for vm_struct
Date
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.stoppa@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 cfd0ac4..2abd540 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -56,6 +56,7 @@ 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 6739420..44c5dfc 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 page_counter;
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 (page_counter = 0; page_counter < area->nr_pages; page_counter++)
+ area->pages[page_counter]->area = area;
+
return addr;

fail:
--
2.9.3
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