From: Marc Lehmann <schmorp@schmorp.de>
To: Nikolay Borisov <nborisov@suse.com>, Filipe Manana <fdmanana@gmail.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: cpu bound I/O behaviour in linux 5.4 (possibly others)
Date: Fri, 14 Feb 2020 13:40:47 +0100 [thread overview]
Message-ID: <20200214124040.GA7686@schmorp.de> (raw)
In-Reply-To: <CAL3q7H7SPyXB+5G6+XtgfviJdBQQSYD1YyJZPX6rbWxhes-+qw@mail.gmail.com> <7a472107-ab87-d787-9f4f-d0d0e148061a@suse.com>
First of all, thanks for the response - and if my mails are somehow
off-topic for the list, also feelf ree to tell me :)
On Fri, Feb 14, 2020 at 01:57:33PM +0200, Nikolay Borisov <nborisov@suse.com> wrote:
> > one core) in top:
>
> So this is a 50tb useful space, right?
Yup, pretty full, too. I also forgot to mention that the vast majority
of files are between 400kB and 2MB, and not, as one might expect from
textgroups, a few kilobytes.
> > [<0>] tree_search_offset.isra.0+0x16a/0x1d0 [btrfs]
>
> This points to freespace cache. One thing that I might suggest is try
Hmm, I did switch to the free space tree on all larger filesystems long
ago, or at least I thought so. I use these mount options on the fs in
question:
rw,noatime,nossd,space_cache=v2,commit=120,subvolid=5,subvol=/
I assume this is the correct way to get it (and your space_cache=2 is a
typo, or an alternative?).
So either I am not switching on the free space tree properly, or it's not
the problem. I did notice major speedups form it in the past, though.
> So you can't deduce that the free space cache is being used, and
> despite being the default, it was not mentioned by Marc if he's not
> using already the free space tree (-o space_cache=v2).
Yes, sorry, it's alwayss hard to strike a balance between needed info and
too much.
> Switching from one to the other might make the problem go away, simply
> because it cause free space to be scanned and build a new cache or
> tree.
So clearing the free space tree might also help? Can I do this while its
mounted using remount or do I haver to umount/mount (or use btrfs check)?
--
The choice of a Deliantra, the free code+content MORPG
-----==- _GNU_ http://www.deliantra.net
----==-- _ generation
---==---(_)__ __ ____ __ Marc Lehmann
--==---/ / _ \/ // /\ \/ / schmorp@schmorp.de
-=====/_/_//_/\_,_/ /_/\_\
next prev parent reply other threads:[~2020-02-14 13:08 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-14 11:30 cpu bound I/O behaviour in linux 5.4 (possibly others) Marc Lehmann
2020-02-14 11:57 ` Nikolay Borisov
2020-02-14 12:20 ` Filipe Manana
2020-02-14 20:07 ` Marc Lehmann
2020-02-14 12:40 ` Marc Lehmann [this message]
2020-02-14 12:36 ` Roman Mamedov
2020-02-14 12:45 ` Marc Lehmann
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