[PATCH 3/7] struct page: add field for vm_struct

When a page is used for virtual memory, it is often necessary to obtain
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, later on.

Signed-off-by: Igor Stoppa <redacted>
---
  include/linux/mm_types.h | 1 +
  mm/vmalloc.c             | 2 ++
  2 files changed, 3 insertions(+)

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 ebff729cc956..61a1ca22b0f6 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c

@@ -1536,6 +1536,7 @@ 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);
  		}
  

@@ -1705,6 +1706,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
  			area->nr_pages = i;
  			goto fail;
  		}
+		page->area = area;
  		area->pages[i] = page;
  		if (gfpflags_allow_blocking(gfp_mask|highmem_mask))
  			cond_resched();