linux-ext4 - Re: EXT4 nodelalloc => back to stone age.

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Message-ID: <20130401155705.16754.31446@localhost.localdomain>
Date:	Mon, 1 Apr 2013 11:57:05 -0400
From:	Chris Mason <chris.mason@...ionio.com>
To:	Chris Mason <chris.mason@...ionio.com>,
	Eric Sandeen <sandeen@...hat.com>,
	Dmitry Monakhov <dmonakhov@...nvz.org>
CC:	ext4 development <linux-ext4@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"axboe@...nel.dk" <axboe@...nel.dk>, Jan Kara <jack@...e.cz>
Subject: Re: EXT4 nodelalloc => back to stone age.

Quoting Chris Mason (2013-04-01 11:45:41)
> Quoting Eric Sandeen (2013-04-01 11:18:51)
> > On 4/1/13 6:06 AM, Dmitry Monakhov wrote:
> > 
> > > 1)Do we really have to use WRITE_SYNC in case of WB_SYNC_ALL ?
> 
> Yes?  The stuff we wait on should be WRITE_SYNC.
> 
> > 
> > ...
> > 
> > > 2) Why don't we have writepages for non delalloc case ?
> > 
> > ...
> > 
> > I'd add:
> > 
> > 3) Why do we have a "nodelalloc" mount option at all?
> > 
> > but then I thought:
> > 
> > Is it also this bad when using the ext4 driver to run an ext3 fs?
> 
> Quick comparison on a single iodrive:

On the theory that writepages is the problem try echo 1 >
/sys/block/xxx/queue/rotational.  With request merging on here in
nodelalloc mode:

dd if=/dev/zero of=foo bs=1M count=1024 conv=fsync,notrunc
1073741824 bytes (1.1 GB) copied, 2.53741 s, 423 MB/s

dd if=/dev/zero of=foo bs=1M count=1024 conv=fsync,notrunc
1073741824 bytes (1.1 GB) copied, 1.37795 s, 779 MB/s

-chris
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