From: Dave Chinner <david@fromorbit.com>
To: Amit Sahrawat <amit.sahrawat83@gmail.com>
Cc: "hch@infradead.org" <hch@infradead.org>,
"xfs@oss.sgi.com" <xfs@oss.sgi.com>
Subject: Re: Preallocation with direct IO?
Date: Sat, 31 Dec 2011 07:43:07 +1100 [thread overview]
Message-ID: <20111230204307.GN23662@dastard> (raw)
In-Reply-To: <CADDb1s18XsCRkjq_spMKx0-4g2H51mRJXn=u=boqUe4TXZw-MQ@mail.gmail.com>
On Fri, Dec 30, 2011 at 08:37:00AM +0530, Amit Sahrawat wrote:
> On Fri, Dec 30, 2011 at 2:27 AM, Dave Chinner <david@fromorbit.com> wrote:
> > On Thu, Dec 29, 2011 at 01:10:49PM +0000, amit.sahrawat83@gmail.com wrote:
> >> Hi, I am using a test setup which is doing write using multiple
> >> threads using direct IO. The buffer size which is used to write is
> >> 512KB. After continously running this for long duration - i
> >> observe that number of extents in each file is getting
> >> huge(2K..4K..). I observed that each extent is of 512KB(aligned to
> >> write buffer size). I wish to have low number of extents(i.e,
> >> reduce fragmentation)... In case of buffered IO- preallocation
> >> works good alongwith the mount option 'allocsize'. Is there
> >> anything which can be done for Direct IO? Please advice for
> >> reducing fragmentation with direct IO.
> >
> > Direct IO does not do any implicit preallocation. The filesystem
> > simply gets out of the way of direct IO as it is assumed you know
> > what you are doing.
> This is the supporting line I was looking for.
> >
> > i.e. you know how to use the fallocate() or ioctl(XFS_IOC_RESVSP64)
> > calls to preallocate space or to set up extent size hints to use
> > larger allocations than the IO being done during syscalls...
> I tried to make use of preallocating space using
> ioctl(XFS_IOC_RESVSP64) - but over time - this is also not working
> well with the Direct I/O.
Without knowing how you are using preallocation, I cannot comment on
this. Can you describe how your application does IO (size,
frequency, location in file, etc) and preallocation (same again), as
well as xfs_bmap -vp <file> output of fragmented files? That way I
have some idea of what your problem is and so might be able to
suggest fixes...
> Is there any call to set up extent size
> also? please update I can try to make use of that also.
`man xfsctl` and search for XFS_IOC_FSSETXATTR.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
_______________________________________________
xfs mailing list
xfs@oss.sgi.com
http://oss.sgi.com/mailman/listinfo/xfs
next prev parent reply other threads:[~2011-12-30 20:43 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-29 13:10 Preallocation with direct IO? amit.sahrawat83
2011-12-29 20:57 ` Dave Chinner
2011-12-30 3:07 ` Amit Sahrawat
2011-12-30 20:43 ` Dave Chinner [this message]
2011-12-31 12:46 ` Amit Sahrawat
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20111230204307.GN23662@dastard \
--to=david@fromorbit.com \
--cc=amit.sahrawat83@gmail.com \
--cc=hch@infradead.org \
--cc=xfs@oss.sgi.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox