readahead: remove the local copy of ra in do_generic_mapping_read()
Fengguang Wu [Tue, 16 Oct 2007 08:24:35 +0000 (01:24 -0700)]
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>

mm/filemap.c

index bbcca45..3c97bdc 100644 (file)
@@ -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)