On Wed, Mar 05, 2014 at 03:13:43PM +0100, Lucas Nussbaum wrote:
> TL;DR: we experience long temporary hangs when doing multiple mount -o
> remount at the same time as other I/O on an ext4 filesystem.
Hi Lukas,
Thanks for this report. Are you willing to try a kernel patch? If
so, could you try and see if this fixes your issue. From looking at
your block trace, I saw a large number of suspicious 4k writes from
the jbd2 layer.
- Ted
commit 137d7cea675fd7d8ff98b7e035fb6516dc4ab220
Author: Theodore Ts'o <tytso@xxxxxxx>
Date: Thu Mar 6 08:56:11 2014 -0500
jbd2: don't write non-commit blocks synchronously
We don't need to write the revoke blocks and descriptor blocks using
WRITE_SYNC, since when we issue the commit block, thos blocks will get
pushed out via REQ_FLUSH. This will allow the journal blocks to be
written in fewer i/o operations (otherwise we end up issuing a whole
series of 4k writes unnecessarily).
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index cf2fc05..fb64629 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -554,7 +554,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
blk_start_plug(&plug);
jbd2_journal_write_revoke_records(journal, commit_transaction,
- &log_bufs, WRITE_SYNC);
+ &log_bufs, WRITE);
blk_finish_plug(&plug);
jbd_debug(3, "JBD2: commit phase 2b\n");
@@ -739,7 +739,7 @@ start_journal_io:
clear_buffer_dirty(bh);
set_buffer_uptodate(bh);
bh->b_end_io = journal_end_buffer_io_sync;
- submit_bh(WRITE_SYNC, bh);
+ submit_bh(WRITE, bh);
}
cond_resched();
stats.run.rs_blocks_logged += bufs;
--
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