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Commit 7ff81078 authored by Fengguang Wu's avatar Fengguang Wu Committed by Linus Torvalds
Browse files

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: default avatarFengguang Wu <wfg@mail.ustc.edu.cn>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6b10c6c9

mm/filemap.c

+9 −11
Original line number Diff line number Diff line
@@ -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)