Re: [Ext2-devel] Re: [PATCH 2/3] ext3 reservation allow turn off for specifed file

[Mingming Cao <cmm@us.ibm.com>]

On Wed, 2004-10-20 at 10:55, Ray Lee wrote:
> On Mon, 2004-10-18 at 18:01 -0700, Mingming Cao wrote:
> > On Mon, 2004-10-18 at 16:42, Andrew Morton wrote:
> > > Applications currently pass a seeky-access hint into the kernel via
> > > posix_fadvise(POSIX_FADV_RANDOM).  It would be nice to hook into that
> 
> [...]
> 
> > Just thought seeky random write application could use the existing ioctl
> > to let the kernel know it does not need reservation at all. Isn't that
> > more straightforward?
> 
> Going the ioctl route seems to imply that userspace would have to do a
> posix_fadvise() call and the ioctl, as opposed to just the fadvise. No?
> I'm betting the fadvise call is a little more portable as well.

Agreed. How about this: add a check in ext3_prepare_write(), if user passed seeky-access hint through posix_fadvise(via check for file->f_ra.ra_pages == 0), if so, close the reservation window.  But we still need previous patch to handle window size 0(no reservation) in reservation code.

Currently the readahead is turned off if the userspace passed a seeky access hint to kernel by POSIX_FADVISE. It would be nice to turn off the block allocation reservation as well for seeky random write.


---

 linux-2.6.9-rc4-mm1-ming/fs/ext3/inode.c |    9 +++++++++
 1 files changed, 9 insertions(+)

diff -puN fs/ext3/inode.c~ext3_turn_off_reservation_by_fadvise fs/ext3/inode.c
--- linux-2.6.9-rc4-mm1/fs/ext3/inode.c~ext3_turn_off_reservation_by_fadvise	2004-10-25 18:25:44.135751800 -0700
+++ linux-2.6.9-rc4-mm1-ming/fs/ext3/inode.c	2004-10-25 18:34:39.501363856 -0700
@@ -1008,6 +1008,15 @@ retry:
 		ret = PTR_ERR(handle);
 		goto out;
 	}
+
+	/*
+	 * if user passed a seeky-access hint to kernel,
+	 * through POSIX_FADV_RANDOM,(file->r_ra.ra_pages is cleared)
+	 * turn off reservation for block allocation correspondingly.
+	 */
+	if (!file->f_ra.ra_pages)
+		atomic_set(&EXT3_I(inode)->i_rsv_window.rsv_goal_size, 0);
+
 	ret = block_prepare_write(page, from, to, ext3_get_block);
 	if (ret)
 		goto prepare_write_failed;

_