Re: large files unnecessary trashing filesystem cache?

[Andrew Morton <akpm@osdl.org>]

Ingo Oeser <ioe-lkml@rameria.de> wrote:
>
> Hi,
> 
> On Wednesday 19 October 2005 13:10, gfiala@s.netic.de wrote:
> > Zitat von Andrew Morton <akpm@osdl.org>:

Please don't edit Cc lines.  Just do reply-to-all.

> > > So I'd also suggest a new resource limit which, if set, is copied into the
> > > applications's file_structs on open().  So you then write a little wrapper
> > > app which does setrlimit()+exec():
> > > 
> > > 	limit-cache-usage -s 1000 my-fave-backup-program <args>
> > > 
> > > Which will cause every file which my-fave-backup-program reads or writes to
> > > be limited to a maximum pagecache residency of 1000 kbytes.
> > 
> > Or make it another 'ulimit' parameter...

That's what I said.  ulimit is the shell interface to resource limits.

> Which is already there: There is an ulimit for "maximum RSS", 
> which is at least a superset of "maximum pagecache residency".

RSS is a quite separate concept from pagecache.

> This is already settable and known by many admins. But AFAIR it is not
> honoured by the kernel completely, right?
> 
> But per file is a much better choice, since this would allow
> concurrent streaming. This is needed to implement timeshifting at least[1].
> 
> So either I miss something or this is no proper solution yet.

I described a couple of ways in which this can be done from userspace with
LD_PRELOAD.