From: Suparna Bhattacharya <suparna@in.ibm.com>
DESC
aio O_DIRECT no readahead
EDESC
From: Daniel McNeil <daniel@osdl.org>
More testing on AIO with O_DIRECT and /dev/raw/. Doing AIO reads was
using a lot more cpu time than using dd on the raw partition even with
the io_queue_wait patch. Found out that aio is doing readahead even
for O_DIRECT. Here's a patch that fixes it.
fs/aio.c | 20 +++++++++++++++++++-
mm/filemap.c | 3 ++-
2 files changed, 21 insertions(+), 2 deletions(-)
diff -puN fs/aio.c~aio-12-readahead fs/aio.c
--- 25/fs/aio.c~aio-12-readahead 2003-09-26 22:22:49.000000000 -0700
+++ 25-akpm/fs/aio.c 2003-09-26 22:22:49.000000000 -0700
@@ -28,6 +28,7 @@
#include <linux/highmem.h>
#include <linux/workqueue.h>
#include <linux/writeback.h>
+#include <linux/pagemap.h>
#include <asm/kmap_types.h>
#include <asm/uaccess.h>
@@ -1350,8 +1351,25 @@ ssize_t aio_setup_iocb(struct kiocb *kio
kiocb->ki_left)))
break;
ret = -EINVAL;
- if (file->f_op->aio_read)
+ if (file->f_op->aio_read) {
+ /*
+ * Do not do readahead for DIRECT i/o
+ */
+ if (!(file->f_flags & O_DIRECT)) {
+ struct address_space *mapping;
+ unsigned long index;
+ unsigned long end;
+
+ mapping = file->f_dentry->d_inode->i_mapping;
+ index = kiocb->ki_pos >> PAGE_CACHE_SHIFT;
+ end = (kiocb->ki_pos + kiocb->ki_left) >>
+ PAGE_CACHE_SHIFT;
+ for (; index < end; index++)
+ page_cache_readahead(mapping,
+ &file->f_ra, file, index);
+ }
kiocb->ki_retry = aio_pread;
+ }
break;
case IOCB_CMD_PWRITE:
ret = -EBADF;
diff -puN mm/filemap.c~aio-12-readahead mm/filemap.c
--- 25/mm/filemap.c~aio-12-readahead 2003-09-26 22:22:49.000000000 -0700
+++ 25-akpm/mm/filemap.c 2003-09-26 22:22:49.000000000 -0700
@@ -663,7 +663,8 @@ void do_generic_mapping_read(struct addr
}
cond_resched();
- page_cache_readahead(mapping, ra, filp, index);
+ if (is_sync_wait(current->io_wait))
+ page_cache_readahead(mapping, ra, filp, index);
nr = nr - offset;
find_page:
_