Merge branch 'master'

1 files changed, 24 insertions, 9 deletions

diff --git a/mm/readahead.c b/mm/readahead.c
index 9f0b98227b41..ba7db816f4c8 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -53,13 +53,24 @@ static inline unsigned long get_min_readahead(struct file_ra_state *ra)
 	return (VM_MIN_READAHEAD * 1024) / PAGE_CACHE_SIZE;
 }
 
+static inline void reset_ahead_window(struct file_ra_state *ra)
+{
+	/*
+	 * ... but preserve ahead_start + ahead_size value,
+	 * see 'recheck:' label in page_cache_readahead().
+	 * Note: We never use ->ahead_size as rvalue without
+	 * checking ->ahead_start != 0 first.
+	 */
+	ra->ahead_size += ra->ahead_start;
+	ra->ahead_start = 0;
+}
+
 static inline void ra_off(struct file_ra_state *ra)
 {
 	ra->start = 0;
 	ra->flags = 0;
 	ra->size = 0;
-	ra->ahead_start = 0;
-	ra->ahead_size = 0;
+	reset_ahead_window(ra);
 	return;
 }
 
@@ -73,10 +84,10 @@ static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
 {
 	unsigned long newsize = roundup_pow_of_two(size);
 
-	if (newsize <= max / 64)
-		newsize = newsize * newsize;
+	if (newsize <= max / 32)
+		newsize = newsize * 4;
 	else if (newsize <= max / 4)
-		newsize = max / 4;
+		newsize = newsize * 2;
 	else
 		newsize = max;
 	return newsize;
@@ -427,8 +438,7 @@ static int make_ahead_window(struct address_space *mapping, struct file *filp,
 		 * congestion.  The ahead window will any way be closed
 		 * in case we failed due to excessive page cache hits.
 		 */
-		ra->ahead_start = 0;
-		ra->ahead_size = 0;
+		reset_ahead_window(ra);
 	}
 
 	return ret;
@@ -521,11 +531,11 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra,
 	 * If we get here we are doing sequential IO and this was not the first
 	 * occurence (ie we have an existing window)
 	 */
-
 	if (ra->ahead_start == 0) {	 /* no ahead window yet */
 		if (!make_ahead_window(mapping, filp, ra, 0))
-			goto out;
+			goto recheck;
 	}
+
 	/*
 	 * Already have an ahead window, check if we crossed into it.
 	 * If so, shift windows and issue a new ahead window.
@@ -537,11 +547,16 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra,
 		ra->start = ra->ahead_start;
 		ra->size = ra->ahead_size;
 		make_ahead_window(mapping, filp, ra, 0);
+recheck:
+		/* prev_page shouldn't overrun the ahead window */
+		ra->prev_page = min(ra->prev_page,
+			ra->ahead_start + ra->ahead_size - 1);
 	}
 
 out:
 	return ra->prev_page + 1;
 }
+EXPORT_SYMBOL_GPL(page_cache_readahead);
 
 /*
  * handle_ra_miss() is called when it is known that a page which should have