Messages in this thread | | | Date | Tue, 17 Feb 2009 13:30:17 +0100 | From | Nick Piggin <> | Subject | Re: set_page_dirty races (was: Re: [patch 2/4] vfs: add set_page_dirty_notag) |
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On Tue, Feb 17, 2009 at 01:05:34PM +0100, Peter Zijlstra wrote: > On Tue, 2009-02-17 at 12:55 +0100, Nick Piggin wrote: > > If nobody thinks it is insane, I'll resend to Andrew in a new thread. > > Right, gup_fast() seems to also respect .write properly,
Phew! :)
> so it would > also be used to balance that. > > I guess gup_fast() would need to use trylock_page(), and fall back to > the slow path when we start taking PG_locked on .write.
Yeah, you're right there. It might also be possible to have a flag somewhere to avoid the lock if the underlying filesystem doesn't have a page_mkwrite or doesn't account dirty... which could avoid the overhead for the common case of anonymous or tmpfs memory.
For gup_fast that pretty much implies an extra page flag I think. But let's not get too worried with details... I don't think put_user_pages hurts, even if it only remains as put_page loop. Just to help reader through the page refcounting.
> I suppose we should start converting a few gup users over to pup before > handing the thing to Andrew, to have at least a few examples in-kernel.
Could do. There are quite a few easy ones.
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