On Wed, 2005-12-14 at 04:12 -0800, Mitchell Blank Jr wrote:
> Alan Cox wrote:
> > But your user space that would add the routes is not so protected so I'm
> > not sure this is actually a solution, more of an extended fudge.
>
> Yes, there's no 100% solution -- no matter how much memory you reserve and
> how many paths you protect if you try hard enough you can come up
> with cases where it'll fail. ("I'm swapping to NFS across a tun/tap
> interface to a custom userland SSL tunnel to a server across a BGP route...")
>
> However, if the 'extended fundge' pushes a problem from "can happen, even
> in a very normal setup" territory to "only happens if you're doing something
> pretty weird" then is it really such a bad thing? I think the cost in code
> complexity looks pretty reasonable.
Yes. This should work fine for cases where you need a limited number of
critical allocation requests to succeed for a short period of time.
> > > +#define SK_CRIT_ALLOC(sk, flags) ((sk->sk_allocation & __GFP_CRITICAL) |
> > > flags)
> >
> > Lots of hidden conditional logic on critical paths.
>
> How expensive is it compared to the allocation itself?
Also, as i said in my other response we could make it a compile-time
configurable option with zero overhead when turned off.
Thanks
Sridhar
>
> > > +#define CRIT_ALLOC(flags) (__GFP_CRITICAL | flags)
> >
> > Pointless obfuscation
>
> Fully agree.
>
> -Mitch
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