linux-kernel - Re: [dm-devel] Re: [PATCH] dm-snapshot: poor copy-on-write performance due to I/O reordering

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <48D9D666.8010402@oss.ntt.co.jp>
Date:	Wed, 24 Sep 2008 14:55:50 +0900
From:	Kazuo Ito <ito.kazuo@....ntt.co.jp>
To:	device-mapper development <dm-devel@...hat.com>
CC:	7eggert@....de, kjamieson@...ast.com, linux-kernel@...r.kernel.org
Subject: Re: [dm-devel] Re: [PATCH] dm-snapshot: poor copy-on-write performance
 due to I/O reordering

Hello,

 > Bodo Eggert wrote:
 >> Kazuo Ito <ito.kazuo@....ntt.co.jp> wrote:
 >>
 >>> Write throughput to LVM snapshot origin volume is an order
 >>> of magnitude slower than those to LV without snapshots or
 >>> snapshot target volumes, especially in the case of sequential
 >>> writes with O_SYNC on.
 >>>
 >>> The following patch originally written by Kevin Jamieson and
 >>> Jan Blunck and slightly modified for the current RCs by myself
 >>> tries to improve the performance by modifying the behaviour
 >>> of kcopyd, so that it pushes back an I/O job to the head of
 >>> the job queue instead of the tail as process_jobs() currently
 >>> does when it has to wait for free pages. This way, write
 >>> requests aren't shuffled to cause extra seeks.
 >>
 >> Did you check for starvation problems, too?

I have twice and four times as many pages allocated
to each kcopyd client without patching the queuing behaviour
and got these figures (MiB/s) -- allocating more buffers doesn't
seem to help much, so I don't think it's memory shortage
that matters here.

test \ # of buffer pages   256(default)      512        1024
  10M dd+fsync, create        16.00          18.60      18.95
  10M dd+fsync, update        16.14          18.39      19.70
100M dd+fsync, create        15.18          18.80      19.29
100M dd+fsync, update        15.28          19.29      19.45

--
> Kazuo Ito, NTT Open Source Software Center
> Phone: +81-3-5860-5125 / FAX: +81-3-5463-5690 / E-mail: 
> ito.kazuo@....ntt.co.jp

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/