Re: [RFC] Event counters [1/3]: Basic counter functionality

Nick Piggin
2006-01-03T05:11:46Z

On Mon, 2006-01-02 at 19:40 -0200, Marcelo Tosatti wrote:

> Nick,
>
> The following patch:
>
> - Moves the lightweight "inc/dec" versions of mod_page_state variants
> to three underscores, making those the default for locations where enough
> locks are held.
>

I guess I was hoping to try to keep it simple, and just have two
variants, the __ version would require the caller to do the locking.
In cases like eg. allocstall, they should happen infrequently enough
that the extra complexity is probably not worth worrying about.

I don't think I commented about the preempt race though (and requirement
to have preempt off from process context), which obviously can be a
problem as you say (though I think things are currently safe?).

> - Make the two-underscore version disable and enable preemption, which
> is required to avoid preempt-related races which can result in missed
> updates.
>
> - Extends the lightweight version usage in page reclaim,
> pte allocation, and a few other codepaths.
>

I guess nr_dirty looks OK in the places it can be put under tree_lock.

nr_page_table_pages is OK because ptl should be held to prevent preempt.

pgrotated and pgactivate should be good because of lru_lock.

Thanks for going through these!

--
SUSE Labs, Novell Inc.

Send instant messages to your online friends http://au.messenger.yahoo.com