Linux-BTRFS Archive on lore.kernel.org
 help / Atom feed
From: Filipe Manana <fdmanana@gmail.com>
To: dsterba@suse.cz, Josef Bacik <josef@toxicpanda.com>,
	Chris Mason <clm@fb.com>, Nikolay Borisov <nborisov@suse.com>,
	linux-btrfs <linux-btrfs@vger.kernel.org>,
	Kernel-team@fb.com
Subject: Re: [PATCH 2/3] btrfs: wakeup cleaner thread when adding delayed iput
Date: Wed, 28 Nov 2018 20:08:02 +0000
Message-ID: <CAL3q7H52+ELQBw4kn7aUJqX+TR=NMFHvtY4QTVvsM0UNJauQvw@mail.gmail.com> (raw)
In-Reply-To: <20181128190633.GZ2842@twin.jikos.cz>

On Wed, Nov 28, 2018 at 7:09 PM David Sterba <dsterba@suse.cz> wrote:
>
> On Tue, Nov 27, 2018 at 03:08:08PM -0500, Josef Bacik wrote:
> > On Tue, Nov 27, 2018 at 07:59:42PM +0000, Chris Mason wrote:
> > > On 27 Nov 2018, at 14:54, Josef Bacik wrote:
> > >
> > > > On Tue, Nov 27, 2018 at 10:26:15AM +0200, Nikolay Borisov wrote:
> > > >>
> > > >>
> > > >> On 21.11.18 г. 21:09 ч., Josef Bacik wrote:
> > > >>> The cleaner thread usually takes care of delayed iputs, with the
> > > >>> exception of the btrfs_end_transaction_throttle path.  The cleaner
> > > >>> thread only gets woken up every 30 seconds, so instead wake it up to
> > > >>> do
> > > >>> it's work so that we can free up that space as quickly as possible.
> > > >>
> > > >> Have you done any measurements how this affects the overall system. I
> > > >> suspect this introduces a lot of noise since now we are going to be
> > > >> doing a thread wakeup on every iput, does this give a chance to have
> > > >> nice, large batches of iputs that  the cost of wake up can be
> > > >> amortized
> > > >> across?
> > > >
> > > > I ran the whole patchset with our A/B testing stuff and the patchset
> > > > was a 5%
> > > > win overall, so I'm inclined to think it's fine.  Thanks,
> > >
> > > It's a good point though, a delayed wakeup may be less overhead.
> >
> > Sure, but how do we go about that without it sometimes messing up?  In practice
> > the only time we're doing this is at the end of finish_ordered_io, so likely to
> > not be a constant stream.  I suppose since we have places where we force it to
> > run that we don't really need this.  IDK, I'm fine with dropping it.  Thanks,
>
> The transaction thread wakes up cleaner periodically (commit interval,
> 30s by default), so the time to process iputs is not unbounded.
>
> I have the same concerns as Nikolay, coupling the wakeup to all delayed
> iputs could result in smaller batches. But some of the callers of
> btrfs_add_delayed_iput might benefit from the extra wakeup, like
> btrfs_remove_block_group, so I don't want to leave the idea yet.

I'm curious, why do you think it would benefit btrfs_remove_block_group()?



-- 
Filipe David Manana,

“Whether you think you can, or you think you can't — you're right.”

  parent reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-21 19:09 [PATCH 0/3] Delayed iput fixes Josef Bacik
2018-11-21 19:09 ` [PATCH 1/3] btrfs: run delayed iputs before committing Josef Bacik
2018-11-26 14:44   ` Nikolay Borisov
2018-11-21 19:09 ` [PATCH 2/3] btrfs: wakeup cleaner thread when adding delayed iput Josef Bacik
2018-11-27  8:26   ` Nikolay Borisov
2018-11-27 19:54     ` Josef Bacik
2018-11-27 19:59       ` Chris Mason
2018-11-27 20:08         ` Josef Bacik
2018-11-28 19:06           ` David Sterba
2018-11-28 19:32             ` Chris Mason
2018-11-28 20:08             ` Filipe Manana [this message]
2018-11-29  0:30               ` Qu Wenruo
2018-11-21 19:09 ` [PATCH 3/3] btrfs: replace cleaner_delayed_iput_mutex with a waitqueue Josef Bacik
2018-11-27  8:29   ` Nikolay Borisov
2018-11-27 20:01     ` Josef Bacik
2018-12-03 16:06 [PATCH 0/3][V2] Delayed iput fixes Josef Bacik
2018-12-03 16:06 ` [PATCH 2/3] btrfs: wakeup cleaner thread when adding delayed iput Josef Bacik
2018-12-04  9:21   ` Nikolay Borisov
2018-12-04 18:18     ` Josef Bacik
2019-01-11 15:21 [PATCH 0/3][V3] Delayed iput fixes Josef Bacik
2019-01-11 15:21 ` [PATCH 2/3] btrfs: wakeup cleaner thread when adding delayed iput Josef Bacik

Reply instructions:

You may reply publically 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='CAL3q7H52+ELQBw4kn7aUJqX+TR=NMFHvtY4QTVvsM0UNJauQvw@mail.gmail.com' \
    --to=fdmanana@gmail.com \
    --cc=Kernel-team@fb.com \
    --cc=clm@fb.com \
    --cc=dsterba@suse.cz \
    --cc=josef@toxicpanda.com \
    --cc=linux-btrfs@vger.kernel.org \
    --cc=nborisov@suse.com \
    /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

Linux-BTRFS Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-btrfs/0 linux-btrfs/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-btrfs linux-btrfs/ https://lore.kernel.org/linux-btrfs \
		linux-btrfs@vger.kernel.org linux-btrfs@archiver.kernel.org
	public-inbox-index linux-btrfs


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-btrfs


AGPL code for this site: git clone https://public-inbox.org/ public-inbox