Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)

Nick Piggin
2007-03-07T14:50:56Z

On Wed, Mar 07, 2007 at 02:53:07PM +0100, Miklos Szeredi wrote:
> > > msync() might never get called and then we're back with the old
> > > behaviour where we can surprise the VM with a ton of dirty pages.
> >
> > But we're root. With your patch, root *can't* do nonlinear writeback
> > well. Ever. With msync, at least you give them enough rope.
>
> Restricting to root doesn't buy you much, nobody wants to be root.
> Restricting to mlock is similarly pointless. UML _will_ want to get
> swapped out if there's no activity.

They could always not use nonlinear, or we could add a ulimit to the
size of nonlinear vaddr allowed.

> Restricting to tmpfs makes sense, but it's probably not what UML
> wants.

I think it is OK. They might want some persistent storage to migrate
or something, but that can always be done by copying from tmpfs to
a block based filesystem.