From: Martin Raiber <martin@urbackup.org>
To: Hans van Kranenburg <hans.van.kranenburg@mendix.com>,
"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: Multiple btrfs-cleaner threads per volume
Date: Thu, 2 Nov 2017 15:26:42 +0000 [thread overview]
Message-ID: <0102015f7d576dad-688908ab-87d9-4715-9626-fb37cfff32e8-000000@eu-west-1.amazonses.com> (raw)
In-Reply-To: <75dfd17b-3f3a-dc22-e069-d68faa33eb8e@mendix.com>
On 02.11.2017 16:10 Hans van Kranenburg wrote:
> On 11/02/2017 04:02 PM, Martin Raiber wrote:
>> snapshot cleanup is a little slow in my case (50TB volume). Would it
>> help to have multiple btrfs-cleaner threads? The block layer underneath
>> would have higher throughput with more simultaneous read/write requests.
> Just curious:
> * How many subvolumes/snapshots are you removing, and what's the
> complexity level (like, how many other subvolumes/snapshots reference
> the same data extents?)
> * Do you see a lot of cpu usage, or mainly a lot of disk I/O? If it's
> disk IO, is it mainly random read IO, or is it a lot of write traffic?
> * What mount options are you running with (from /proc/mounts)?
It is a single block device, so not a multi-device btrfs, so
optimizations in that area wouldn't help. It is a UrBackup system with
about 200 snapshots per client. 20009 snapshots total. UrBackup reflinks
files between them, but btrfs-cleaner doesn't use much CPU (so it
doesn't seem like the backref walking is the problem). btrfs-cleaner is
probably limited mainly by random read/write IO. The device has a cache,
so parallel accesses would help, as some of them may hit the cache.
Looking at the code it seems easy enough to do. Question is if there are
any obvious reasons why this wouldn't work (like some lock etc.).
next prev parent reply other threads:[~2017-11-02 15:26 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-02 15:02 Multiple btrfs-cleaner threads per volume Martin Raiber
2017-11-02 15:07 ` Austin S. Hemmelgarn
2017-11-02 15:10 ` Hans van Kranenburg
2017-11-02 15:26 ` Martin Raiber [this message]
2017-11-02 16:56 ` Hans van Kranenburg
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