Re: [PATCH RFC v3 0/6] Intruduce nfsrahead

[Trond Myklebust <trondmy@hammerspace.com>]

On Wed, 2022-03-23 at 21:32 +0000, Matthew Wilcox wrote:
> On Wed, Mar 23, 2022 at 05:18:35PM -0300, Thiago Becker wrote:
> > Recent changes in the linux kernel caused NFS readahead to default
> > to
> > 128 from the previous default of 15 * rsize. This causes
> > performance
> > penalties to some read-heavy workloads, which can be fixed by
> > tuning the readahead for that given mount.
> 
> Which recent changes?  Something in NFS or something in the VFS/MM?
> Did you even think about asking a wider audience than the NFS mailing
> list?  I only happened to notice this while I was looking for
> something
> else, otherwise I would never have seen it.  The responses from other
> people to your patches were right; you're trying to do this all
> wrong.
> 
> Let's start out with a bug report instead of a solution.  What
> changed
> and when?

I believe Thiago is talking about the changes introduced by commit
c128e575514c "NFS: Optimise the default readahead size" (i.e. we're
talking about Linux 5.4).

...and yes, as the commit description notes, users who want to change
the default can do so using the standard sysfs mechanism.
AFAICS, all this is doing is providing a toolset to allow users to more
easily set up and edit the udev scripts that will automate these
settings.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com