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From: Dave Chinner <david@fromorbit.com>
To: Avi Kivity <avi@scylladb.com>
Cc: Eric Sandeen <sandeen@sandeen.net>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Gandalf Corvotempesta <gandalf.corvotempesta@gmail.com>,
	linux-xfs@vger.kernel.org
Subject: Re: agcount for 2TB, 4TB and 8TB drives
Date: Tue, 17 Oct 2017 09:31:58 +1100	[thread overview]
Message-ID: <20171016223158.GK15067@dastard> (raw)
In-Reply-To: <10d04693-02ef-427f-95fe-cc7bcaf3ec6f@scylladb.com>

On Mon, Oct 16, 2017 at 01:00:32PM +0300, Avi Kivity wrote:
> On 10/16/2017 01:00 AM, Dave Chinner wrote:
> >On Sun, Oct 15, 2017 at 12:36:03PM +0300, Avi Kivity wrote:
> >>On 10/15/2017 01:42 AM, Dave Chinner wrote:
> >>>On Fri, Oct 13, 2017 at 11:13:24AM +0300, Avi Kivity wrote:
> >>Even better would be if XFS would detect the sequential write and
> >>start allocating ahead of it.
> >That's what delayed allocation does with buffered IO. We
> >specifically do not do that with direct IO because it's direct IO
> >and we only do exactly what the IO the user submits requires us to
> >do.
> >
> >As it is, I'm not sure that it would gain us anything over extent
> >size hints because they are effectively doing exactly the same thing
> >(i.e.  allocate ahead) on every write that hits a hole beyond
> >EOF when extending the file....
> 
> If I understand correctly, you do get momentary serialization when
> you cross a hint boundary, while with allocate ahead, you would not.

Allocate ahead still requires a threshold to be crossed to trigger
allocation. So it doesn't get rid of allocation, it just changes
what IO triggers it.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

  reply	other threads:[~2017-10-16 22:32 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-06  8:46 agcount for 2TB, 4TB and 8TB drives Gandalf Corvotempesta
2017-10-06 15:38 ` Darrick J. Wong
2017-10-06 16:18   ` Eric Sandeen
2017-10-06 22:20     ` Dave Chinner
2017-10-06 22:21       ` Eric Sandeen
2017-10-09  8:05         ` Avi Kivity
2017-10-09 11:23           ` Dave Chinner
2017-10-09 15:46             ` Avi Kivity
2017-10-09 22:03               ` Dave Chinner
2017-10-10  9:07                 ` Avi Kivity
2017-10-10 22:55                   ` Dave Chinner
2017-10-13  8:13                     ` Avi Kivity
2017-10-14 22:42                       ` Dave Chinner
2017-10-15  9:36                         ` Avi Kivity
2017-10-15 22:00                           ` Dave Chinner
2017-10-16 10:00                             ` Avi Kivity
2017-10-16 22:31                               ` Dave Chinner [this message]
2017-10-18  7:31                             ` Christoph Hellwig

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