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Subject[PATCH 06/10] 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>
---
mm/filemap.c | 20 +++++++++-----------
1 file changed, 9 insertions(+), 11 deletions(-)
--- linux-2.6.22-rc6-mm1.orig/mm/filemap.c
+++ linux-2.6.22-rc6-mm1/mm/filemap.c
@@ -863,7 +863,7 @@ static void shrink_readahead_size_eio(st
* 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,
@@ -877,12 +877,11 @@ void do_generic_mapping_read(struct addr
unsigned long prev_index;
unsigned int prev_offset;
int error;
- struct file_ra_state ra = *_ra;

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;

@@ -897,7 +896,7 @@ 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))
@@ -905,7 +904,7 @@ find_page:
}
if (PageReadahead(page)) {
page_cache_async_readahead(mapping,
- &ra, filp, page,
+ ra, filp, page,
index, last_index - index);
}
if (!PageUptodate(page))
@@ -1016,7 +1015,7 @@ readpage:
}
unlock_page(page);
error = -EIO;
- shrink_readahead_size_eio(filp, &ra);
+ shrink_readahead_size_eio(filp, ra);
goto readpage_error;
}
unlock_page(page);
@@ -1053,10 +1052,9 @@ 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 (filp)
--
-
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