Re: + drop-pagecache.patch added to -mm tree

[Christoph Hellwig <hch@infradead.org>]

On Thu, Dec 29, 2005 at 05:54:08PM +0800, Coywolf Qi Hunt wrote:
> 2005/12/2, akpm@osdl.org <akpm@osdl.org>:
> >
> > The patch titled
> >
> >      drop-pagecache
> >
> > has been added to the -mm tree.  Its filename is
> >
> >      drop-pagecache.patch
> >
> >
> > From: Andrew Morton <akpm@osdl.org>
> >
> > Add /proc/sys/vm/drop-pagecache.  When written to, this will cause the kernel
> > to discard as much pagecache and reclaimable slab objects as it can.
> >
> > It won't drop dirty data, so the user should run `sync' first.
> >
> > Caveats:
> >
> > a) Holds inode_lock for exorbitant amounts of time.
> >
> > b) Needs to be taught about NUMA nodes: propagate these all the way through
> >    so the discarding can be controlled on a per-node basis.
> >
> > c) The pagecache shrinking and slab shrinking should probably have separate
> >    controls.

d) it is a total mess.

A lot of code for something that you shouldn't do
except for benchmarking.  If people see problems where pagecache data isn't
dropped enough we should fix the VM instead of adding code that just bloats
the kernel more.