readahead: data structure and routines
Extend struct file_ra_state to support the on-demand readahead logic. Also
define some helpers for it.
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Cc: Steven Pratt <slpratt@austin.ibm.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 75dd16e..9a5f562 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -695,6 +695,10 @@
/*
* Track a single file's readahead state
+ *
+ * ================#============|==================#==================|
+ * ^ ^ ^ ^
+ * file_ra_state.la_index .ra_index .lookahead_index .readahead_index
*/
struct file_ra_state {
unsigned long start; /* Current window */
@@ -704,6 +708,12 @@
unsigned long prev_index; /* Cache last read() position */
unsigned long ahead_start; /* Ahead window */
unsigned long ahead_size;
+
+ pgoff_t la_index; /* enqueue time */
+ pgoff_t ra_index; /* begin offset */
+ pgoff_t lookahead_index; /* time to do next readahead */
+ pgoff_t readahead_index; /* end offset */
+
unsigned long ra_pages; /* Maximum readahead window */
unsigned long mmap_hit; /* Cache hit stat for mmap accesses */
unsigned long mmap_miss; /* Cache miss stat for mmap accesses */
@@ -712,6 +722,60 @@
#define RA_FLAG_MISS 0x01 /* a cache miss occured against this file */
#define RA_FLAG_INCACHE 0x02 /* file is already in cache */
+/*
+ * Measuring read-ahead sizes.
+ *
+ * |----------- readahead size ------------>|
+ * ===#============|==================#=====================|
+ * |------- invoke interval ------>|-- lookahead size -->|
+ */
+static inline unsigned long ra_readahead_size(struct file_ra_state *ra)
+{
+ return ra->readahead_index - ra->ra_index;
+}
+
+static inline unsigned long ra_lookahead_size(struct file_ra_state *ra)
+{
+ return ra->readahead_index - ra->lookahead_index;
+}
+
+static inline unsigned long ra_invoke_interval(struct file_ra_state *ra)
+{
+ return ra->lookahead_index - ra->la_index;
+}
+
+/*
+ * Check if @index falls in the readahead windows.
+ */
+static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index)
+{
+ return (index >= ra->la_index &&
+ index < ra->readahead_index);
+}
+
+/*
+ * Where is the old read-ahead and look-ahead?
+ */
+static inline void ra_set_index(struct file_ra_state *ra,
+ pgoff_t la_index, pgoff_t ra_index)
+{
+ ra->la_index = la_index;
+ ra->ra_index = ra_index;
+}
+
+/*
+ * Where is the new read-ahead and look-ahead?
+ */
+static inline void ra_set_size(struct file_ra_state *ra,
+ unsigned long ra_size, unsigned long la_size)
+{
+ ra->readahead_index = ra->ra_index + ra_size;
+ ra->lookahead_index = ra->ra_index + ra_size - la_size;
+}
+
+unsigned long ra_submit(struct file_ra_state *ra,
+ struct address_space *mapping, struct file *filp);
+
struct file {
/*
* fu_list becomes invalid after file_free is called and queued via
