[PATCH v6 43/51] mm: Support storing shadow entries for THPs

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>

If the page is being replaced with a NULL, we can do a single store that
erases the entire range of indices.  Otherwise we have to use a loop to
store one shadow entry in each index.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 mm/filemap.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 78f888d028c5..17db007f0277 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -120,22 +120,27 @@ static void page_cache_delete(struct address_space *mapping,
 				   struct page *page, void *shadow)
 {
 	XA_STATE(xas, &mapping->i_pages, page->index);
-	unsigned int nr = 1;
+	unsigned int i, nr = 1, entries = 1;
 
 	mapping_set_update(&xas, mapping);
 
 	/* hugetlb pages are represented by a single entry in the xarray */
 	if (!PageHuge(page)) {
-		xas_set_order(&xas, page->index, compound_order(page));
-		nr = compound_nr(page);
+		entries = nr = thp_nr_pages(page);
+		if (!shadow) {
+			xas_set_order(&xas, page->index, thp_order(page));
+			entries = 1;
+		}
 	}
 
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(PageTail(page), page);
-	VM_BUG_ON_PAGE(nr != 1 && shadow, page);
 
-	xas_store(&xas, shadow);
-	xas_init_marks(&xas);
+	for (i = 0; i < entries; i++) {
+		xas_store(&xas, shadow);
+		xas_init_marks(&xas);
+		xas_next(&xas);
+	}
 
 	page->mapping = NULL;
 	/* Leave page->index set: truncation lookup relies upon it */
-- 
2.26.2