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Message-ID: <20071007104658.655565e3@laptopd505.fenrus.org> Date: Sun, 7 Oct 2007 10:46:58 -0700 From: Arjan van de Ven <arjan@...radead.org> To: Jeremy Fitzhardinge <jeremy@...p.org> Cc: Ingo Molnar <mingo@...e.hu>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: lockdep: how to tell it multiple pte locks is OK? On Sun, 7 Oct 2007 10:17:47 -0700 Jeremy Fitzhardinge <jeremy@...p.org> wrote: > > On Oct 7, 2007, at 9:58 AM, Arjan van de Ven wrote: > > > On Sat, 06 Oct 2007 23:31:33 -0700 > > > >> I'm presume I'm the first person to try holding multiple pte locks > >> at once, so there's no existing locking order for these locks. I'm > >> always traversing and locking the pagetable in virtual address > >> order (and this seems like a sane-enough rule for anyone else who > >> wants to hold multiple pte locks). > > > > I'm not sure that's a valid assumption in light of things like > > sharing pagetables between processes etc etc.. > > (granted, that one is out of tree right now but I still hope it'll > > go in some day:) > > Well, yes, but that will take some thought about how split pte locks > will work anyway (or more specifically, fork will probably just end > up reusing the pte pages and avoid the need to do any > cross-pagetable pte locking anyway, though I guess that will be > deferred to COW handling). > > So are you saying I should pass up the opportunity to optimise a > relatively hot path (fork/exec/exit) because it will need some > further thought if/when shared ptes get implemented? s/implemented/merged/ :) IN fact shared pagetables are already there for hugepages. For small pages it's a patch at this point. > Doesn't seem > like a good tradeoff... no I'm not saying that. I'm just saying that I'm worried about the locking robustness of your trick in general. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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