[Gluster-devel] How commonly applications make use of fadvise?

[Niels de Vos]

On Fri, Aug 11, 2017 at 12:47:47AM -0400, Raghavendra Gowdappa wrote:
> Hi all,
> 
> In a conversation between me, Milind and Csaba, Milind pointed out
> fadvise(2) [1] and its potential benefits to Glusterfs' caching
> translators like read-ahead etc. After discussing about it, we agreed
> that our performance translators can leverage the hints to provide
> better performance. Now the question is how commonly applications
> actually provide hints? Is it something that is used quite frequently?
> If yes, we can think of implementing this in glusterfs (probably
> kernel-fuse too?). If no, there is not much of an advantage in
> spending our energies here. Your inputs will help us to prioritize
> this feature.

If functionality like this is available, we would add support in
libgfapi.so as well. NFS-Ganesha is prepared for consuming this
(fsal_obj_ops->io_advise), so applications running on top of NFS will
benefit. I failed to see if the standard Samba/vfs can use it.

A quick check in QEMU does not suggest it is used by the block drivers.

I don't think Linux/FUSE supports fadvise though. So this is an
oppertunity for a Gluster developer to get their name in the Linux
kernel :-) Feature additions like this have been done before by us, and
we should continue where we can. It is a relatively easy entry for
contributing to the Linux kernel.
 
> [1] https://linux.die.net/man/2/fadvise

As well as local man-pages for fadvise64/posix_fadvise.

Showing that we have support for this, suggests that the filesystem
becomes more mature and gains advanced features. This should impress
users and might open up more interest for certain (HPC?) use-cases.

Thanks,
Niels


> 
> regards,
> Raghavendra
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