Re: large files unnecessary trashing filesystem cache?

[gfiala@s.netic.de]

Zitat von Andrew Morton <akpm@osdl.org>:

> An obvious approach would be an LD_PRELOAD thingy which modifies read() and
> write(), perhaps controlled via an environment variable.  AFAIK nobody has
> even attempted this.

Sounds interesting.

> A decent kernel implementation would be to add a max_resident_pages to
> struct file_struct and to use that to perform drop-behind within read() and
> write().  That's a bit of arithmetic and a call to
> invalidate_mapping_pages().  The userspace interface to that could be a
> linux-specific extension to posix_fadvise() or to fcntl().

Would still like to have a way to configure a "default file policy/heuristics"
for the system, just like i can choose IO-scheduler.

> 
> But that still requires that all the applications be modified.
> 
> 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...