Re: [RFC PATCH 0/3] page count lock for simpler put_page

[Michel Lespinasse <walken@google.com>]

On Fri, Aug 12, 2011 at 10:27 AM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
> Or maybe I make rcu_cookie_gp_elapsed() take only one cookie and
> compare it to the current cookie.  This would save a bit of code in
> the TINY cases:
>
>        rcu_get_gp_cookie(&pagep->rcucookie);
>        . . .
>
>        if (!rcu_cookie_gp_elapsed(&pagep->rcucookie))
>                synchronize_rcu();

Agree this looks nicer that having the second cookie on the stack. As
you said, this does not allow us to compare two past points in time,
but I really don't see a use case for that.

> How long would there normally be between recording the cookie and
> checking for the need for a grace period?  One disk access?  One HZ?
> Something else?

I would expect >>10 seconds in the normal case ? I'm not sure how much
lower this may get in adverse workloads. Andrea ?

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.

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