Messages in this thread | | | Date | Tue, 3 Jan 2006 08:11:06 -0200 | From | Marcelo Tosatti <> | Subject | Re: [RFC] Event counters [1/3]: Basic counter functionality |
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On Tue, Jan 03, 2006 at 04:11:46PM +1100, Nick Piggin wrote: > 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.
I see - one point is that the two/three underscore versions make it clear that preempt is required, though, but it might be a bit over-complicated as you say.
Well, its up to you - please rearrange the patch as you wish and merge up?
> In cases like eg. allocstall, they should happen infrequently enough > that the extra complexity is probably not worth worrying about.
True, but it reduces kernel code, which is always good.
> 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?).
"I think it should not be racy because the function should always be called with the page table lock held, which disables preempt. I guess the comment should be explicit about that as well."
Yes, you're right! My bad.
> > - 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!
There's still probably a few more counters but the ones covered till now should be the most significant ones performance-wise. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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