1 files changed, 75 insertions, 0 deletions
diff --git a/mm/readahead.c b/mm/readahead.c
index 5b423ecc99f1..d589f147f4c2 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -638,3 +638,78 @@ SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
 {
 	return ksys_readahead(fd, offset, count);
 }
+
+/**
+ * readahead_expand - Expand a readahead request
+ * @ractl: The request to be expanded
+ * @new_start: The revised start
+ * @new_len: The revised size of the request
+ *
+ * Attempt to expand a readahead request outwards from the current size to the
+ * specified size by inserting locked pages before and after the current window
+ * to increase the size to the new window.  This may involve the insertion of
+ * THPs, in which case the window may get expanded even beyond what was
+ * requested.
+ *
+ * The algorithm will stop if it encounters a conflicting page already in the
+ * pagecache and leave a smaller expansion than requested.
+ *
+ * The caller must check for this by examining the revised @ractl object for a
+ * different expansion than was requested.
+ */
+void readahead_expand(struct readahead_control *ractl,
+		      loff_t new_start, size_t new_len)
+{
+	struct address_space *mapping = ractl->mapping;
+	struct file_ra_state *ra = ractl->ra;
+	pgoff_t new_index, new_nr_pages;
+	gfp_t gfp_mask = readahead_gfp_mask(mapping);
+
+	new_index = new_start / PAGE_SIZE;
+
+	/* Expand the leading edge downwards */
+	while (ractl->_index > new_index) {
+		unsigned long index = ractl->_index - 1;
+		struct page *page = xa_load(&mapping->i_pages, index);
+
+		if (page && !xa_is_value(page))
+			return; /* Page apparently present */
+
+		page = __page_cache_alloc(gfp_mask);
+		if (!page)
+			return;
+		if (add_to_page_cache_lru(page, mapping, index, gfp_mask) < 0) {
+			put_page(page);
+			return;
+		}
+
+		ractl->_nr_pages++;
+		ractl->_index = page->index;
+	}
+
+	new_len += new_start - readahead_pos(ractl);
+	new_nr_pages = DIV_ROUND_UP(new_len, PAGE_SIZE);
+
+	/* Expand the trailing edge upwards */
+	while (ractl->_nr_pages < new_nr_pages) {
+		unsigned long index = ractl->_index + ractl->_nr_pages;
+		struct page *page = xa_load(&mapping->i_pages, index);
+
+		if (page && !xa_is_value(page))
+			return; /* Page apparently present */
+
+		page = __page_cache_alloc(gfp_mask);
+		if (!page)
+			return;
+		if (add_to_page_cache_lru(page, mapping, index, gfp_mask) < 0) {
+			put_page(page);
+			return;
+		}
+		ractl->_nr_pages++;
+		if (ra) {
+			ra->size++;
+			ra->async_size++;
+		}
+	}
+}
+EXPORT_SYMBOL(readahead_expand);