From: Jan Kara <jack@suse.cz>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: clm@fb.com, dsterba@suse.com, jack@suse.cz,
linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org, Jan Kara <jack@suze.cz>,
Davidlohr Bueso <dbueso@suse.de>
Subject: Re: [PATCH] btrfs: always write superblocks synchronously
Date: Wed, 3 May 2017 10:36:15 +0200 [thread overview]
Message-ID: <20170503083615.GC10084@quack2.suse.cz> (raw)
In-Reply-To: <20170502162813.4299-1-dave@stgolabs.net>
On Tue 02-05-17 09:28:13, Davidlohr Bueso wrote:
> Commit b685d3d65ac7 "block: treat REQ_FUA and REQ_PREFLUSH as
> synchronous" removed REQ_SYNC flag from WRITE_FUA implementation.
> Since REQ_FUA and REQ_FLUSH flags are stripped from submitted IO
> when the disk doesn't have volatile write cache and thus effectively
> make the write async. This was seen to cause performance hits up
> to 90% regression in disk IO related benchmarks such as reaim and
> dbench[1].
>
> Fix the problem by making sure the first superblock write is also
> treated as synchronous since they can block progress of the
> journalling (commit, log syncs) machinery and thus the whole filesystem.
>
> [1] https://www.spinics.net/lists/linux-ext4/msg56238.html
>
> Fixes: b685d3d65ac (block: treat REQ_FUA and REQ_PREFLUSH as synchronous)
> Cc: stable <stable@vger.kernel.org>
> Cc: Jan Kara <jack@suze.cz>
> Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
I wasn't patient enough and already sent the fix as part of my series
fixing other filesystems [1]. It also fixes one more place in btrfs that
needs REQ_SYNC to return to the original behavior.
[1] https://www.spinics.net/lists/linux-btrfs/msg65022.html
Honza
> ---
> fs/btrfs/disk-io.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index 061c1d1f774f..51b2fd8ceccb 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -3468,7 +3468,7 @@ static int write_dev_supers(struct btrfs_device *device,
> * to go down lazy.
> */
> if (i == 0)
> - ret = btrfsic_submit_bh(REQ_OP_WRITE, REQ_FUA, bh);
> + ret = btrfsic_submit_bh(REQ_OP_WRITE, REQ_FUA | REQ_SYNC, bh);
> else
> ret = btrfsic_submit_bh(REQ_OP_WRITE, REQ_SYNC, bh);
> if (ret)
> --
> 2.12.0
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2017-05-03 8:36 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-02 16:28 [PATCH] btrfs: always write superblocks synchronously Davidlohr Bueso
2017-05-03 8:36 ` Jan Kara [this message]
2017-05-03 14:55 ` Chris Mason
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170503083615.GC10084@quack2.suse.cz \
--to=jack@suse.cz \
--cc=clm@fb.com \
--cc=dave@stgolabs.net \
--cc=dbueso@suse.de \
--cc=dsterba@suse.com \
--cc=jack@suze.cz \
--cc=linux-btrfs@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=stable@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).