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

[Lukáš Czerner]

On Fri, 27 Jun 2014, Matthias Schniedermeyer wrote:

> Date: Fri, 27 Jun 2014 10:41:39 +0200
> From: Matthias Schniedermeyer <ms@xxxxxxx>
> To: Luká? Czerner <lczerner@xxxxxxxxxx>
> Cc: Artem Bityutskiy <dedekind1@xxxxxxxxx>,
>     Bernd Schubert <bernd.schubert@xxxxxxxxxxxxxxxxxx>,
>     Dave Chinner <david@xxxxxxxxxxxxx>, Thomas Knauth <thomas.knauth@xxxxxx>,
>     David Rientjes <rientjes@xxxxxxxxxx>,
>     Maksym Planeta <mcsim.planeta@xxxxxxxxx>,
>     Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx,
>     linux-kernel@xxxxxxxxxxxxxxx
> 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.
> 
> 
> 
> 
>