readahead: code cleanup

Rename file_ra_state.prev_page to prev_index and file_ra_state.offset to
prev_offset.  Also update of prev_index in do_generic_mapping_read() is now
moved close to the update of prev_offset.

[wfg@mail.ustc.edu.cn: fix it]
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: WU Fengguang <wfg@mail.ustc.edu.cn>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 21 insertions, 20 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0949e243b8b9..55a74ffa7e3b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -696,13 +696,13 @@ struct file_ra_state {
         unsigned long size;
         unsigned long flags;            /* ra flags RA_FLAG_xxx*/
         unsigned long cache_hit;        /* cache hit count*/
-        unsigned long prev_page;        /* Cache last read() position */
+        unsigned long prev_index;       /* Cache last read() position */
         unsigned long ahead_start;      /* Ahead window */
         unsigned long ahead_size;
         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 */
-        unsigned int offset;            /* Offset where last read() ended in a page */
+        unsigned int prev_offset;       /* Offset where last read() ended in a page */
 };
 #define RA_FLAG_MISS 0x01       /* a cache miss occured against this file */
 #define RA_FLAG_INCACHE 0x02    /* file is already in cache */
diff --git a/mm/filemap.c b/mm/filemap.c
index 07f5b77114a3..5631d6b2a62d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -877,8 +877,8 @@ void do_generic_mapping_read(struct address_space *mapping,
         cached_page = NULL;
         index = *ppos >> PAGE_CACHE_SHIFT;
         next_index = index;
-        prev_index = ra.prev_page;
-        prev_offset = ra.offset;
+        prev_index = ra.prev_index;
+        prev_offset = ra.prev_offset;
         last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
         offset = *ppos & ~PAGE_CACHE_MASK;
 
@@ -947,7 +947,8 @@ page_ok:
                 offset += ret;
                 index += offset >> PAGE_CACHE_SHIFT;
                 offset &= ~PAGE_CACHE_MASK;
-                prev_offset = ra.offset = offset;
+                prev_offset = offset;
+                ra.prev_offset = offset;
 
                 page_cache_release(page);
                 if (ret == nr && desc->count)
diff --git a/mm/readahead.c b/mm/readahead.c
index 0a6fed9d365c..9861e883fe57 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -37,7 +37,7 @@ void
 file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
 {
         ra->ra_pages = mapping->backing_dev_info->ra_pages;
-        ra->prev_page = -1;
+        ra->prev_index = -1;
 }
 EXPORT_SYMBOL_GPL(file_ra_state_init);
 
@@ -202,19 +202,19 @@ out:
  * size:        Number of pages in that read
  *              Together, these form the "current window".
  *              Together, start and size represent the `readahead window'.
- * prev_page:   The page which the readahead algorithm most-recently inspected.
+ * prev_index:  The page which the readahead algorithm most-recently inspected.
  *              It is mainly used to detect sequential file reading.
  *              If page_cache_readahead sees that it is again being called for
  *              a page which it just looked at, it can return immediately without
  *              making any state changes.
- * offset:      Offset in the prev_page where the last read ended - used for
+ * offset:      Offset in the prev_index where the last read ended - used for
  *              detection of sequential file reading.
  * ahead_start,
  * ahead_size:  Together, these form the "ahead window".
  * ra_pages:    The externally controlled max readahead for this fd.
  *
  * When readahead is in the off state (size == 0), readahead is disabled.
- * In this state, prev_page is used to detect the resumption of sequential I/O.
+ * In this state, prev_index is used to detect the resumption of sequential I/O.
  *
  * The readahead code manages two windows - the "current" and the "ahead"
  * windows.  The intent is that while the application is walking the pages
@@ -417,7 +417,7 @@ static int make_ahead_window(struct address_space *mapping, struct file *filp,
         ra->ahead_size = get_next_ra_size(ra);
         ra->ahead_start = ra->start + ra->size;
 
-        block = force || (ra->prev_page >= ra->ahead_start);
+        block = force || (ra->prev_index >= ra->ahead_start);
         ret = blockable_page_cache_readahead(mapping, filp,
                         ra->ahead_start, ra->ahead_size, ra, block);
 
@@ -469,13 +469,13 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra,
          * We avoid doing extra work and bogusly perturbing the readahead
          * window expansion logic.
          */
-        if (offset == ra->prev_page && --req_size)
+        if (offset == ra->prev_index && --req_size)
                 ++offset;
 
-        /* Note that prev_page == -1 if it is a first read */
-        sequential = (offset == ra->prev_page + 1);
-        ra->prev_page = offset;
-        ra->offset = 0;
+        /* Note that prev_index == -1 if it is a first read */
+        sequential = (offset == ra->prev_index + 1);
+        ra->prev_index = offset;
+        ra->prev_offset = 0;
 
         max = get_max_readahead(ra);
         newsize = min(req_size, max);
@@ -484,7 +484,7 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra,
         if (newsize == 0 || (ra->flags & RA_FLAG_INCACHE))
                 goto out;
 
-        ra->prev_page += newsize - 1;
+        ra->prev_index += newsize - 1;
 
         /*
          * Special case - first read at start of file. We'll assume it's
@@ -540,18 +540,18 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra,
          * we get called back on the first page of the ahead window which
          * will allow us to submit more IO.
          */
-        if (ra->prev_page >= ra->ahead_start) {
+        if (ra->prev_index >= ra->ahead_start) {
                 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,
+                /* prev_index shouldn't overrun the ahead window */
+                ra->prev_index = min(ra->prev_index,
                         ra->ahead_start + ra->ahead_size - 1);
         }
 
 out:
-        return ra->prev_page + 1;
+        return ra->prev_index + 1;
 }
 EXPORT_SYMBOL_GPL(page_cache_readahead);