On 06/03/2015 07:05 PM, Kirill A. Shutemov wrote:
Let's define page_mapped() to be true for compound pages if any
sub-pages of the compound page is mapped (with PMD or PTE).
On other hand page_mapcount() return mapcount for this particular small
page.
This will make cases like page_get_anon_vma() behave correctly once we
allow huge pages to be mapped with PTE.
Most users outside core-mm should use page_mapcount() instead of
page_mapped().
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
[...]
@@ -917,10 +917,21 @@ static inline pgoff_t page_file_index(struct page *page)
/*
* Return true if this page is mapped into pagetables.
+ * For compound page it returns true if any subpage of compound page is mapped.
*/
-static inline int page_mapped(struct page *page)
+static inline bool page_mapped(struct page *page)
{
- return atomic_read(&(page)->_mapcount) + compound_mapcount(page) >= 0;
+ int i;
+ if (likely(!PageCompound(page)))
+ return atomic_read(&page->_mapcount) >= 0;
+ page = compound_head(page);
+ if (compound_mapcount(page))
Same optimization opportunity as I pointed out in previous patch for
page_mapcount().
+ return true;
+ for (i = 0; i < hpage_nr_pages(page); i++) {
+ if (atomic_read(&page[i]._mapcount) >= 0)
+ return true;
+ }
+ return true;
}
/*
diff --git a/mm/filemap.c b/mm/filemap.c
index cb41cf3069d2..c6cf03303ded 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -202,7 +202,7 @@ void __delete_from_page_cache(struct page *page, void *shadow)
__dec_zone_page_state(page, NR_FILE_PAGES);
if (PageSwapBacked(page))
__dec_zone_page_state(page, NR_SHMEM);
- BUG_ON(page_mapped(page));
+ VM_BUG_ON_PAGE(page_mapped(page), page);
/*
* At this point page must be either written or cleaned by truncate.
--
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