Re: page cache: Store only head pages in i_pages

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Sat, Mar 23, 2019 at 07:50:15PM -0400, Qian Cai wrote:
> On 3/22/19 11:38 PM, Matthew Wilcox wrote:
> > On Fri, Mar 22, 2019 at 04:12:48PM -0400, Qian Cai wrote:
> >> FYI, every thing involve swapping seems triggered a panic now since this patch.
> 
> Yes, it works.

Thanks for testing.  Kirill suggests this would be a better fix:

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 41858a3744b4..9718393ae45b 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -334,10 +334,12 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
 
 static inline struct page *find_subpage(struct page *page, pgoff_t offset)
 {
+	unsigned long index = page_index(page);
+
 	VM_BUG_ON_PAGE(PageTail(page), page);
-	VM_BUG_ON_PAGE(page->index > offset, page);
-	VM_BUG_ON_PAGE(page->index + compound_nr(page) <= offset, page);
-	return page - page->index + offset;
+	VM_BUG_ON_PAGE(index > offset, page);
+	VM_BUG_ON_PAGE(index + compound_nr(page) <= offset, page);
+	return page - index + offset;
 }
 
 struct page *find_get_entry(struct address_space *mapping, pgoff_t offset);