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

[Mingming Cao]

On Mon, 2004-10-25 at 13:33, Mingming Cao wrote:
> 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.

The previous patch could re-open the reservation in the case user then
switch back to POSIX_FADV_NORMAL or POSIZ_FADV_SEQUENTAIL. Updated
version included. We set the window size to -1 if the user pass the
POSIX_FADV_RANDOM, instead of 0, to differentiate the case when user
really want to close the window by ioctl.  We could re-open the window
only when user pass the POSIX_FADV_SEQUENTAIL (or POSIX_FADV_NORMAL
hint) and the window was closed because of previous seeky access hint.

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/balloc.c |    2 +-
 linux-2.6.9-rc4-mm1-ming/fs/ext3/inode.c  |   17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

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 21:43:16.194964928 -0700
@@ -1001,6 +1001,7 @@ static int ext3_prepare_write(struct fil
 	int ret, needed_blocks = ext3_writepage_trans_blocks(inode);
 	handle_t *handle;
 	int retries = 0;
+	int windowsz = 0;
 
 retry:
 	handle = ext3_journal_start(inode, needed_blocks);
@@ -1008,6 +1009,22 @@ 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.
+	 *
+	 * Otherwise, if user switch back to POSIX_FADV_SEQUENTIAL or
+	 * POSIX_FADV_NORMAL, re-open the reservation window.
+	 */
+	windowsz = atomic_read(&EXT3_I(inode)->i_rsv_window.rsv_goal_size);
+	if ((windowsz > 0) && (!file->f_ra.ra_pages))
+		atomic_set(&EXT3_I(inode)->i_rsv_window.rsv_goal_size, -1);
+	if ((windowsz == -1) && file->f_ra.ra_pages)
+		atomic_set(&EXT3_I(inode)->i_rsv_window.rsv_goal_size,
+					EXT3_DEFAULT_RESERVE_BLOCKS);
+
 	ret = block_prepare_write(page, from, to, ext3_get_block);
 	if (ret)
 		goto prepare_write_failed;
diff -puN fs/ext3/balloc.c~ext3_turn_off_reservation_by_fadvise fs/ext3/balloc.c
--- linux-2.6.9-rc4-mm1/fs/ext3/balloc.c~ext3_turn_off_reservation_by_fadvise	2004-10-25 21:23:05.152071432 -0700
+++ linux-2.6.9-rc4-mm1-ming/fs/ext3/balloc.c	2004-10-25 21:24:48.136415432 -0700
@@ -1154,7 +1154,7 @@ int ext3_new_block(handle_t *handle, str
 	struct ext3_sb_info *sbi;
 	struct reserve_window_node *my_rsv = NULL;
 	struct reserve_window_node *rsv = &EXT3_I(inode)->i_rsv_window;
-	unsigned short windowsz = 0;
+	int windowsz = 0;
 #ifdef EXT3FS_DEBUG
 	static int goal_hits, goal_attempts;
 #endif

_

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