Hi,
I run some barrier tests over device-mapper (which currently doesn't
support barrier bio at all) and even if I set barrier=1 in ext3 mount,
there is never any bio with barrier flag... (in 2.6.27-rc)
How is the barrier=1 flag supposed to work in ext3 (JBD) now?
See:
If you specify barrier=1, JFS_BARRIER flag is set in ext3_init_journal_params
journal->j_flags |= JFS_BARRIER;
Now, journal_write_commit_record is called and this happens:
if (journal->j_flags & JFS_BARRIER) {
set_buffer_ordered(bh);
barrier_done = 1;
}
ret = sync_dirty_buffer(bh);
if (barrier_done)
clear_buffer_ordered(bh);
if (ret == -EOPNOTSUPP && barrier_done) {
...
>From this code I expect that EOPNOTSUPP is returned if barrier is not
supported (yes, that exactly does device-mapper now without barrier patches).
But it *never* happens because:
sync_dirty_buffer always calls
submit_bh(WRITE_SYNC, bh)
and in submit_bh is this test:
if (buffer_ordered(bh) && (rw == WRITE))
rw = WRITE_BARRIER;
but there is rw == WRITE_SYNC, not WRITE !
So the barrier flag for bio is never set and normal sync write
is performed.
Why it isn't done like in attached patch? Is it intentional or it is bug?
I think it was caused by change in this commit:
commit 18ce3751ccd488c78d3827e9f6bf54e6322676fb
Author: Jens Axboe <jens.axboe@xxxxxxxxxx>
Date: Tue Jul 1 09:07:34 2008 +0200
Properly notify block layer of sync writes
Milan
--
Set BIO_RW_BARRIER flag even for submit_bh sync write request.
Signed-off-by: Milan Broz <mbroz@xxxxxxxxxx>
---
fs/buffer.c | 8 ++++----
1 files changed, 4 insertions(+), 4 deletions(-)
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2926,16 +2926,16 @@ int submit_bh(int rw, struct buffer_head * bh)
BUG_ON(!buffer_mapped(bh));
BUG_ON(!bh->b_end_io);
- if (buffer_ordered(bh) && (rw == WRITE))
- rw = WRITE_BARRIER;
-
/*
* Only clear out a write error when rewriting, should this
* include WRITE_SYNC as well?
*/
- if (test_set_buffer_req(bh) && (rw == WRITE || rw == WRITE_BARRIER))
+ if (test_set_buffer_req(bh) && rw == WRITE)
clear_buffer_write_io_error(bh);
+ if (buffer_ordered(bh) && ((rw & RW_MASK) == WRITE))
+ rw |= (1 << BIO_RW_BARRIER);
+
/*
* from here on down, it's all bio -- do the initial mapping,
* submit_bio -> generic_make_request may further map this bio around
--
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