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SubjectRe: 2.5.62-mm3 - no X for me
Dave McCracken <dmccr@us.ibm.com> wrote:
>
>
> --On Tuesday, February 25, 2003 01:55:37 -0800 Andrew Morton
> <akpm@digeo.com> wrote:
>
> > Ah, thank you.
> >
> > kernel BUG at mm/rmap.c:248!
> >
> > The fickle finger of fate points McCrackenwards.
>
> Yep. He tripped over my sanity check that pages not marked anon actually
> have a real mapping pointer. Apparently X allocates a page that should be
> marked anon but isn't.

Wonder where that came from?

> My main reason for adding the anon flag was to prove to myself that the
> mapping pointer can be trusted. Apparently it can, generally, but it looks
> like I haven't successfully tracked down all the places that should set it.
> It looks like anon pages can come from random sources, so it might be an
> impossible task to find them all.

Yes, the debug check is important at this time.

> I know you said you like the idea of having the flag, but I think the
> cleanest fix would be to change the check from
>
> if (PageAnon(page))
> to
> if (page->mapping && !PageSwapCache(page))

Well I'm not particularly overjoyed by the flag. What I liked was that we
have a place where we can implement anonymous page counting, so we get
another interesting number in /proc/meminfo. Minor point.

> Or I could set the anon flag based on that test. I know page flags are
> getting scarce, so I'm leaning toward removing the flag entirely.
>
> What would you recommend?

Keep the flag for now, find the escaped page under X, remove the flag later?

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