3 files changed, 18 insertions, 1 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 45689621a851..be87edcaba06 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -87,6 +87,9 @@ struct inodes_stat_t {
  */
 #define FMODE_NOCMTIME          ((__force fmode_t)2048)
 
+/* Expect random access pattern */
+#define FMODE_RANDOM            ((__force fmode_t)4096)
+
 /*
  * The below are the various read and write types that we support. Some of
  * them include behavioral modifiers that send information down to the
diff --git a/mm/fadvise.c b/mm/fadvise.c
index e43359214f6f..8d723c9e8b75 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -77,12 +77,20 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
         switch (advice) {
         case POSIX_FADV_NORMAL:
                 file->f_ra.ra_pages = bdi->ra_pages;
+                spin_lock(&file->f_lock);
+                file->f_mode &= ~FMODE_RANDOM;
+                spin_unlock(&file->f_lock);
                 break;
         case POSIX_FADV_RANDOM:
-                file->f_ra.ra_pages = 0;
+                spin_lock(&file->f_lock);
+                file->f_mode |= FMODE_RANDOM;
+                spin_unlock(&file->f_lock);
                 break;
         case POSIX_FADV_SEQUENTIAL:
                 file->f_ra.ra_pages = bdi->ra_pages * 2;
+                spin_lock(&file->f_lock);
+                file->f_mode &= ~FMODE_RANDOM;
+                spin_unlock(&file->f_lock);
                 break;
         case POSIX_FADV_WILLNEED:
                 if (!mapping->a_ops->readpage) {
diff --git a/mm/readahead.c b/mm/readahead.c
index 033bc135a41f..337b20e946f6 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -501,6 +501,12 @@ void page_cache_sync_readahead(struct address_space *mapping,
         if (!ra->ra_pages)
                 return;
 
+        /* be dumb */
+        if (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);
 }