Messages in this thread | | | Date | Wed, 4 Apr 2007 12:24:07 +0200 | From | Nick Piggin <> | Subject | Re: [rfc] no ZERO_PAGE? |
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On Wed, Apr 04, 2007 at 10:45:39AM +0100, Hugh Dickins wrote: > On Wed, 4 Apr 2007, Nick Piggin wrote: > > On Fri, Mar 30, 2007 at 04:40:48AM +0200, Nick Piggin wrote: > > > > > > Well it would make life easier if we got rid of ZERO_PAGE completely, > > > which I definitely wouldn't complain about ;) > > Yes, I love this approach too. > > > > > So, what bad things (apart from my bugs in untested code) happen > > if we do this? We can actually go further, and probably remove the > > ZERO_PAGE completely (just need an extra get_user_pages flag or > > something for the core dumping issue). > > Some things will go faster (no longer needing a separate COW fault > on the read-protected ZERO_PAGE), some things will go slower and use > more memory. The open question is whether anyone will notice those > regressions: I'm hoping they won't, I'm afraid they will. And though > we'll see each as a program doing "something stupid", as in the Altix > case Robin showed to drive us here, we cannot just ignore it.
Sure. Agreed.
> > Shall I do a more complete patchset and ask Andrew to give it a > > run in -mm? > > I'd like you to: I didn't study the fragment below, it's really all > uses of the ZERO_PAGE that I'd like to see go, then we see who shouts.
Yeah, they are basically pretty trivial to remove. I'll do a more complete patch now that I know you like the approach.
> It's quite likely that the patch would have to be reverted: don't > bother to remove the allocations of ZERO_PAGE in each architecture > at this stage, too much nuisance going back and forth on those.
OK.
> Leave ZERO_PAGE as configurable, default off for testing, buried > somewhere like under EMBEDDED? It's much more attractive just to > remove the old code, and reintroduce it if there's a demand; but > leaving it under config would make it easy to restore, and if > there's trouble with removing ZERO_PAGE, we might later choose > to disable it at the high end but enable it at the low. What > would you prefer?
Ooh, the one with more '-' signs in the diff ;)
No, you have a point, but if we have to ask people to recompile with CONFIG_ZERO_PAGE, then it isn't much harder to ask them to apply a patch first.
But for a potential mainline merge, maybe starting with a CONFIG option is a good idea -- defaulting to off, and we could start by turning it on just in -rc kernels for a few releases, to get a bit more confidence? - 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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