Branch HEAD

b=14483
detect stride IO mode in read-ahead.
i=adilger,nikita

lustre/ChangeLog

@@ -785,6 +785,11 @@ Details    : Port llog reference couting and some llog cleanups from b1_6
              (bug 10800) into HEAD, for protect from panic and access to already
 	     free llog structures.
 
+Severity   : normal
+Bugzilla   : 14483
+Description: Detect stride IO mode in read-ahead 
+Details    : When a client does stride read, read-ahead should detect that and
+	     read-ahead pages according to the detected stride pattern. 
 
 --------------------------------------------------------------------------------
 

lustre/llite/llite_internal.h

@@ -390,6 +390,27 @@ struct ll_readahead_state {
          * protected by ->ras_lock.
          */
         struct list_head ras_read_beads;
+        /* 
+         * The following 3 items are used for detecting the stride I/O
+         * mode. 
+ 	 * In stride I/O mode, 
+         * ...............|-----data-----|****gap*****|--------|******|.... 
+         *    offset      |-stride_pages-|-stride_gap-| 
+         * ras_stride_offset = offset;
+         * ras_stride_length = stride_pages + stride_gap;
+         * ras_stride_pages = stride_pages;
+         * Note: all these three items are counted by pages.
+         */
+        unsigned long ras_stride_length;
+        unsigned long ras_stride_pages;
+        pgoff_t ras_stride_offset;
+        /* 
+         * number of consecutive stride request count, and it is similar as
+         * ras_consecutive_requests, but used for stride I/O mode.
+         * Note: only more than 2 consecutive stride request are detected,
+         * stride read-ahead will be enable
+         */
+        unsigned long ras_consecutive_stride_requests;
 };
 
 struct ll_file_dir {