Re: [PATCH] sysctl: Add a feature to drop caches selectively

Lukáš Czerner
2014-06-27T09:05:07Z

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1823 bytes --]

On Fri, 27 Jun 2014, Matthias Schniedermeyer wrote:

> Date: Fri, 27 Jun 2014 10:41:39 +0200
> From: Matthias Schniedermeyer <ms@citd.de>
> To: Luká? Czerner <lczerner@redhat.com>
> Cc: Artem Bityutskiy <dedekind1@gmail.com>,
> Bernd Schubert <bernd.schubert@itwm.fraunhofer.de>,
> Dave Chinner <david@fromorbit.com>, Thomas Knauth <thomas.knauth@gmx.de>,
> David Rientjes <rientjes@google.com>,
> Maksym Planeta <mcsim.planeta@gmail.com>,
> Alexander Viro <viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org,
> linux-kernel@vger.kernel.org
> Subject: Re: [PATCH] sysctl: Add a feature to drop caches selectively
>
> On 26.06.2014 13:57, Luká? Czerner wrote:
>
> > > So if the authors want to sell this new interface (in whatever form) to
> > > the kernel community, they should start with providing a solid use-case,
> > > with some more details, explore alternatives and show how the
> > > alternatives do not work for them.
> >
> > Yes please, let's see some solid use-case for this.
>
> Personally i would want it to verify files after copying them:
> Especially while moving files:
> - Copy a file
> - <drop cache>
> - Verify that it really is correct on stable storage
> - Remove original file

I assume you're using cp to copy a file, not your own program. In
that case can we make cp optionally use direct io ? It seems that it
would solve your problem in very elegant way.

-Lukas

>
> Currently i choose either of the 3 ways:
> - drop_caches
> - umount/mount
> - Write more data than memory in machine (Which is only an
> approximnation and you have to verify in the same order the files were
> written, so it is likely that any cache was thrashed in the meantime)
>
> But having a way to selectivly "destory" the cache of a file would make
> this task easier.
>
>
>
>
>