readahead: remove the local copy of ra in do_generic_mapping_read()

The local copy of ra in do_generic_mapping_read() can now go away.

It predates readanead(req_size).  In a time when the readahead code was called
on *every* single page.  Hence a local has to be made to reduce the chance of
the readahead state being overwritten by a concurrent reader.  More details
in: Linux: Random File I/O Regressions In 2.6
<http://kerneltrap.org/node/3039>

Cc: Nick Piggin <nickpiggin@yahoo.com.au>
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>

1 files changed, 9 insertions, 11 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index bbcca456d8a6..3c97bdc74a85 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -859,7 +859,7 @@ static void shrink_readahead_size_eio(struct file *filp,
  * It may be NULL.
  */
 void do_generic_mapping_read(struct address_space *mapping,
-                             struct file_ra_state *_ra,
+                             struct file_ra_state *ra,
                              struct file *filp,
                              loff_t *ppos,
                              read_descriptor_t *desc,
@@ -874,13 +874,12 @@ void do_generic_mapping_read(struct address_space *mapping,
         unsigned int prev_offset;
         struct page *cached_page;
         int error;
-        struct file_ra_state ra = *_ra;
 
         cached_page = NULL;
         index = *ppos >> PAGE_CACHE_SHIFT;
         next_index = index;
-        prev_index = ra.prev_pos >> PAGE_CACHE_SHIFT;
-        prev_offset = ra.prev_pos & (PAGE_CACHE_SIZE-1);
+        prev_index = ra->prev_pos >> PAGE_CACHE_SHIFT;
+        prev_offset = ra->prev_pos & (PAGE_CACHE_SIZE-1);
         last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
         offset = *ppos & ~PAGE_CACHE_MASK;
 
@@ -895,7 +894,7 @@ find_page:
                 page = find_get_page(mapping, index);
                 if (!page) {
                         page_cache_sync_readahead(mapping,
-                                        &ra, filp,
+                                        ra, filp,
                                         index, last_index - index);
                         page = find_get_page(mapping, index);
                         if (unlikely(page == NULL))
@@ -903,7 +902,7 @@ find_page:
                 }
                 if (PageReadahead(page)) {
                         page_cache_async_readahead(mapping,
-                                        &ra, filp, page,
+                                        ra, filp, page,
                                         index, last_index - index);
                 }
                 if (!PageUptodate(page))
@@ -1014,7 +1013,7 @@ readpage:
                                 }
                                 unlock_page(page);
                                 error = -EIO;
-                                shrink_readahead_size_eio(filp, &ra);
+                                shrink_readahead_size_eio(filp, ra);
                                 goto readpage_error;
                         }
                         unlock_page(page);
@@ -1054,10 +1053,9 @@ no_cached_page:
         }
 
 out:
-        *_ra = ra;
-        _ra->prev_pos = prev_index;
-        _ra->prev_pos <<= PAGE_CACHE_SHIFT;
-        _ra->prev_pos |= prev_offset;
+        ra->prev_pos = prev_index;
+        ra->prev_pos <<= PAGE_CACHE_SHIFT;
+        ra->prev_pos |= prev_offset;
 
         *ppos = ((loff_t)index << PAGE_CACHE_SHIFT) + offset;
         if (cached_page)