[PATCH 2/4] page_cache_readahead: remove duplicated code

[Oleg Nesterov <oleg@tv-sign.ru>]

Cases "no ahead window" and "crossed into ahead window"
can be unified.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 2.6.11-rc2/mm/readahead.c~	2005-01-25 14:28:22.000000000 +0300
+++ 2.6.11-rc2/mm/readahead.c	2005-01-25 15:17:13.000000000 +0300
@@ -483,43 +483,24 @@ page_cache_readahead(struct address_spac
 	 * occurence (ie we have an existing window)
 	 */
 
-	if (ra->ahead_start == 0) {	 /* no ahead window yet */
-		ra->ahead_size = get_next_ra_size(ra->size, max, min,
-						  &ra->flags);
-		ra->ahead_start = ra->start + ra->size;
-		block = ((offset + newsize -1) >= ra->ahead_start);
-		if (!blockable_page_cache_readahead(mapping, filp,
-		    ra->ahead_start, ra->ahead_size, ra, block)) {
-			/* A read failure in blocking mode, implies pages are
-			 * all cached. So we can safely assume we have taken
-			 * care of all the pages requested in this call. A read
-			 * failure in non-blocking mode, implies we are reading
-			 * more pages than requested in this call.  So we safely
-			 * assume we have taken care of all the pages requested
-			 * in this call.
-			 *
-			 * Just reset the ahead window in case we failed due to
-			 * congestion.  The ahead window will any way be closed
-			 * in case we failed due to exessive page cache hits.
-			 */
-			ra->ahead_start = 0;
-			ra->ahead_size = 0;
-			goto out;
-		}
-	}
 	/*
-	 * Already have an ahead window, check if we crossed into it.
+	 * Check if we crossed into ahead window.
 	 * If so, shift windows and issue a new ahead window.
 	 * Only return the #pages that are in the current window, so that
 	 * we get called back on the first page of the ahead window which
 	 * will allow us to submit more IO.
 	 */
 	if ((offset + newsize - 1) >= ra->ahead_start) {
-		ra->start = ra->ahead_start;
-		ra->size = ra->ahead_size;
-		ra->ahead_start = ra->ahead_start + ra->ahead_size;
-		ra->ahead_size = get_next_ra_size(ra->ahead_size,
-						  max, min, &ra->flags);
+		/* Check if we already have an ahead window */
+		if (ra->ahead_start != 0) {
+			ra->start = ra->ahead_start;
+			ra->size = ra->ahead_size;
+		}
+
+		ra->ahead_size = get_next_ra_size(ra->size, max, min,
+							&ra->flags);
+		ra->ahead_start = ra->start + ra->size;
+
 		block = ((offset + newsize - 1) >= ra->ahead_start);
 		if (!blockable_page_cache_readahead(mapping, filp,
 			ra->ahead_start, ra->ahead_size, ra, block)) {