readahead: sanify file_ra_state names

Rename some file_ra_state variables and remove some accessors.

It results in much simpler code.
Kudos to Rusty!

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
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>

2 files changed, 31 insertions, 98 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 29cb32d3a849..d33beadd9a43 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -695,16 +695,12 @@ struct fown_struct {
 
 /*
  * Track a single file's readahead state
- *
- *  ================#============|==================#==================|
- *                  ^            ^                  ^                  ^
- *  file_ra_state.la_index    .ra_index   .lookahead_index   .readahead_index
  */
 struct file_ra_state {
-        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 */
+        pgoff_t start;                  /* where readahead started */
+        unsigned long size;             /* # of readahead pages */
+        unsigned long async_size;       /* do asynchronous readahead when
+                                           there are only # of pages ahead */
 
         unsigned long ra_pages;         /* Maximum readahead window */
         unsigned long mmap_hit;         /* Cache hit stat for mmap accesses */
@@ -714,59 +710,14 @@ struct file_ra_state {
 };
 
 /*
- * 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;
+        return (index >= ra->start &&
+                index <  ra->start + ra->size);
 }
 
-/*
- * 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
diff --git a/mm/readahead.c b/mm/readahead.c
index 3d262bb738a9..39bf45d43320 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -253,21 +253,16 @@ unsigned long max_sane_readahead(unsigned long nr)
 /*
  * Submit IO for the read-ahead request in file_ra_state.
  */
-unsigned long ra_submit(struct file_ra_state *ra,
+static unsigned long ra_submit(struct file_ra_state *ra,
                        struct address_space *mapping, struct file *filp)
 {
-        unsigned long ra_size;
-        unsigned long la_size;
         int actual;
 
-        ra_size = ra_readahead_size(ra);
-        la_size = ra_lookahead_size(ra);
         actual = __do_page_cache_readahead(mapping, filp,
-                                        ra->ra_index, ra_size, la_size);
+                                        ra->start, ra->size, ra->async_size);
 
         return actual;
 }
-EXPORT_SYMBOL_GPL(ra_submit);
 
 /*
  * Set the initial window size, round to next power of 2 and square
@@ -296,7 +291,7 @@ static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
 static unsigned long get_next_ra_size(struct file_ra_state *ra,
                                                 unsigned long max)
 {
-        unsigned long cur = ra->readahead_index - ra->ra_index;
+        unsigned long cur = ra->size;
         unsigned long newsize;
 
         if (cur < max / 16)
@@ -313,28 +308,21 @@ static unsigned long get_next_ra_size(struct file_ra_state *ra,
  * The fields in struct file_ra_state represent the most-recently-executed
  * readahead attempt:
  *
- *                    |-------- last readahead window -------->|
- *       |-- application walking here -->|
- * ======#============|==================#=====================|
- *       ^la_index    ^ra_index          ^lookahead_index      ^readahead_index
- *
- * [ra_index, readahead_index) represents the last readahead window.
- *
- * [la_index, lookahead_index] is where the application would be walking(in
- * the common case of cache-cold sequential reads): the last window was
- * established when the application was at la_index, and the next window will
- * be bring in when the application reaches lookahead_index.
+ *                        |<----- async_size ---------|
+ *     |------------------- size -------------------->|
+ *     |==================#===========================|
+ *     ^start             ^page marked with PG_readahead
  *
  * To overlap application thinking time and disk I/O time, we do
  * `readahead pipelining': Do not wait until the application consumed all
  * readahead pages and stalled on the missing page at readahead_index;
- * Instead, submit an asynchronous readahead I/O as early as the application
- * reads on the page at lookahead_index. Normally lookahead_index will be
- * equal to ra_index, for maximum pipelining.
+ * Instead, submit an asynchronous readahead I/O as soon as there are
+ * only async_size pages left in the readahead window. Normally async_size
+ * will be equal to size, for maximum pipelining.
  *
  * In interleaved sequential reads, concurrent streams on the same fd can
  * be invalidating each other's readahead state. So we flag the new readahead
- * page at lookahead_index with PG_readahead, and use it as readahead
+ * page at (start+size-async_size) with PG_readahead, and use it as readahead
  * indicator. The flag won't be set on already cached pages, to avoid the
  * readahead-for-nothing fuss, saving pointless page cache lookups.
  *
@@ -363,24 +351,21 @@ ondemand_readahead(struct address_space *mapping,
                    unsigned long req_size)
 {
         unsigned long max;      /* max readahead pages */
-        pgoff_t ra_index;       /* readahead index */
-        unsigned long ra_size;  /* readahead size */
-        unsigned long la_size;  /* lookahead size */
         int sequential;
 
         max = ra->ra_pages;
         sequential = (offset - ra->prev_index <= 1UL) || (req_size > max);
 
         /*
-         * Lookahead/readahead hit, assume sequential access.
+         * It's the expected callback offset, assume sequential access.
          * Ramp up sizes, and push forward the readahead window.
          */
-        if (offset && (offset == ra->lookahead_index ||
-                        offset == ra->readahead_index)) {
-                ra_index = ra->readahead_index;
-                ra_size = get_next_ra_size(ra, max);
-                la_size = ra_size;
-                goto fill_ra;
+        if (offset && (offset == (ra->start + ra->size - ra->async_size) ||
+                        offset == (ra->start + ra->size))) {
+                ra->start += ra->size;
+                ra->size = get_next_ra_size(ra, max);
+                ra->async_size = ra->size;
+                goto readit;
         }
 
         /*
@@ -399,24 +384,21 @@ ondemand_readahead(struct address_space *mapping,
          *      - oversize random read
          * Start readahead for it.
          */
-        ra_index = offset;
-        ra_size = get_init_ra_size(req_size, max);
-        la_size = ra_size > req_size ? ra_size - req_size : ra_size;
+        ra->start = offset;
+        ra->size = get_init_ra_size(req_size, max);
+        ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
 
         /*
-         * Hit on a lookahead page without valid readahead state.
+         * Hit on a marked page without valid readahead state.
          * E.g. interleaved reads.
          * Not knowing its readahead pos/size, bet on the minimal possible one.
          */
         if (hit_readahead_marker) {
-                ra_index++;
-                ra_size = min(4 * ra_size, max);
+                ra->start++;
+                ra->size = get_next_ra_size(ra, max);
         }
 
-fill_ra:
-        ra_set_index(ra, offset, ra_index);
-        ra_set_size(ra, ra_size, la_size);
-
+readit:
         return ra_submit(ra, mapping, filp);
 }