---

yaml
---
r: 29764
b: refs/heads/master
c: 76d42bd
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 78dbe706e22f54bce61571ad837238382e1ba5f9
+refs/heads/master: 76d42bd96984832c4ea8bc8cbd74e496ac31409e

trunk/mm/filemap.c

@@ -828,6 +828,32 @@ grab_cache_page_nowait(struct address_space *mapping, unsigned long index)
 }
 EXPORT_SYMBOL(grab_cache_page_nowait);
 
+/*
+ * CD/DVDs are error prone. When a medium error occurs, the driver may fail
+ * a _large_ part of the i/o request. Imagine the worst scenario:
+ *
+ *      ---R__________________________________________B__________
+ *         ^ reading here                             ^ bad block(assume 4k)
+ *
+ * read(R) => miss => readahead(R...B) => media error => frustrating retries
+ * => failing the whole request => read(R) => read(R+1) =>
+ * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
+ * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
+ * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
+ *
+ * It is going insane. Fix it by quickly scaling down the readahead size.
+ */
+static void shrink_readahead_size_eio(struct file *filp,
+					struct file_ra_state *ra)
+{
+	if (!ra->ra_pages)
+		return;
+
+	ra->ra_pages /= 4;
+	printk(KERN_WARNING "Reducing readahead size to %luK\n",
+			ra->ra_pages << (PAGE_CACHE_SHIFT - 10));
+}
+
 /**
  * do_generic_mapping_read - generic file read routine
  * @mapping:	address_space to be read
@@ -985,6 +1011,7 @@ void do_generic_mapping_read(struct address_space *mapping,
 				}
 				unlock_page(page);
 				error = -EIO;
+				shrink_readahead_size_eio(filp, &ra);
 				goto readpage_error;
 			}
 			unlock_page(page);
@@ -1522,6 +1549,7 @@ struct page *filemap_nopage(struct vm_area_struct *area,
 	 * Things didn't work out. Return zero to tell the
 	 * mm layer so, possibly freeing the page cache page first.
 	 */
+	shrink_readahead_size_eio(file, ra);
 	page_cache_release(page);
 	return NULL;
 }