Re: XFS: possible memory allocation deadlock in kmem_alloc

[Carlos Maiolino <cmaiolino@redhat.com>]

On Mon, May 30, 2016 at 04:48:36PM +0800, baotiao wrote:
>    how can I set the extent size hint to a file with command line?
> 
>    I have google for a lot, but I can't find a answer
> 

It can be set with xfs_io, like:

xfs_io -c "extsize 8m" <file>   # To set an extent size hint of 8m

Although, it only works if the file is empty, or more specific, the file must
not have any extents allocated
>    ----------------------------------------
> 
>    Github: [1]https://github.com/baotiao
>    Blog: [2]http://baotiao.github.io
>    Stackoverflow: [3]http://stackoverflow.com/users/634415/baotiao
>    Linkedin: [4]http://www.linkedin.com/profile/view?id=145231990
> 
>    On May 30, 2016, at 13:04, Dave Chinner <[5]david@fromorbit.com> wrote:
> 
>    On Mon, May 30, 2016 at 12:45:07PM +0800, baotiao wrote:
> 
>      This machine is running for qemu,  the file is qemu qcow file type
>      [root@w-openstack20
>      /data/nova/instances/7898b630-c4ef-49ab-9ce9-3735e090c282]# file
>      disk
>      disk: QEMU QCOW Image (v3), has backing file (path
>      /data/nova/instances/_base/3f27393376152ac352b2d85703011e38517e),
>      429496729600 bytes
> 
>    Oh, you're using delta/snapshot based qcow images. That, by it's
>    very nature, generates fragmented image files as they are a delta
>    over the backing file.
>    ....
> 
>      actual 48421430, ideal 20716, fragmentation factor 99.96%
>      How can I solve this problem, what do you suggest me to do?
> 
>    Use a extent size hint (say 1-8MB) for your qcow2 image files so that
>    they don't fragment badly as they are written to.
>    Cheers,
>    Dave.
>    --
>    Dave Chinner
>    [6]david@fromorbit.com
> 
> References
> 
>    1. https://github.com/baotiao
>    2. http://baotiao.github.io/
>    3. http://stackoverflow.com/users/634415/baotiao
>    4. http://www.linkedin.com/profile/view?id=145231990
>    5. mailto:david@fromorbit.com
>    6. mailto:david@fromorbit.com

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-- 
Carlos

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