Re: [Ext2-devel] Re: [PATCH 2/3] ext3 reservation allow turn offfor specifed file

[Andrew Morton]

Mingming Cao <cmm@xxxxxxxxxx> wrote:
>
> > I wonder how important this optimisation really is?  I bet no applications
>  > are using posix_fadvise(POSIX_FADV_RANDOM) anyway.
>  > 
>  I don't know if there is application using the POSIX_FADV_RANDOM. No? If
>  this is the truth, I think we don't need this optimization at present.
>  Logically reservation does not benefit seeky random write, but there is
>  no benchmark showing performance issue so far. We have already provided
>  ways for applications turn off reservation through the existing ioctl
>  for specified file and -o noreservation mount option for the whole
>  filesystem.

Well we definitely don't want to be encouraging application developers to be
adding ext3-specific ioctls.  So we need to work out if any applications
can get significant benefit from manually disabling reservations and if
so, wire up fadvise() into filesystems and do it that way.

Do you know if disabling reservations helps any workloads?
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