1 files changed, 19 insertions, 0 deletions

diff --git a/mm/readahead.c b/mm/readahead.c
index aa1aa2345235..dfa9a1a03a11 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -9,6 +9,7 @@
 
 #include <linux/kernel.h>
 #include <linux/fs.h>
+#include <linux/gfp.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/blkdev.h>
@@ -501,6 +502,12 @@ void page_cache_sync_readahead(struct address_space *mapping,
         if (!ra->ra_pages)
                 return;
 
+        /* be dumb */
+        if (filp && (filp->f_mode & FMODE_RANDOM)) {
+                force_page_cache_readahead(mapping, filp, offset, req_size);
+                return;
+        }
+
         /* do read-ahead */
         ondemand_readahead(mapping, ra, filp, false, offset, req_size);
 }
@@ -547,5 +554,17 @@ page_cache_async_readahead(struct address_space *mapping,
 
         /* do read-ahead */
         ondemand_readahead(mapping, ra, filp, true, offset, req_size);
+
+#ifdef CONFIG_BLOCK
+        /*
+         * Normally the current page is !uptodate and lock_page() will be
+         * immediately called to implicitly unplug the device. However this
+         * is not always true for RAID conifgurations, where data arrives
+         * not strictly in their submission order. In this case we need to
+         * explicitly kick off the IO.
+         */
+        if (PageUptodate(page))
+                blk_run_backing_dev(mapping->backing_dev_info, NULL);
+#endif
 }
 EXPORT_SYMBOL_GPL(page_cache_async_readahead);