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SubjectRe: [PATCH 9/12] memcg allocate all page_cgroup at boot
On Fri, 26 Sep 2008 14:54:22 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> > > There is a SwapCache which is referred from 2 process, A, B.
> > > A maps it.
> > > B doesn't maps it.
> > >
> > > And now, process A exits.
> > >
> > > CPU0(process A) CPU1 (process B)
> > >
> > > zap_pte_range()
> > > => page remove from rmap => charge() (do_swap_page)
> > > => set page->mapcount->0
> > > => uncharge() => set page->mapcount=1
> > >
> > > This race is what patch 12/12 is fixed.
> > > This only happens on cursed SwapCache.
> > >
> > Sorry, my brain seems to be sleeping.. above page_mapped() check doesn't
> > help this situation. Maybe this page_mapped() check is not necessary
> > because it's of no use.
> >
> > I think this kind of problem will not be fixed until we handle SwapCache.
> >
> I've not fully understood yet what [12/12] does, but if we handle
> swapcache properly, [12/12] would become unnecessary?
>
Maybe yes. we treat swapcache under lock_page().

> If so, how about handling swapcache instead of adding new interface?
> I think it can be done independent of mem+swap.
>
Hmm, worth to be considered. But I'll reuse the interface itself for othres
(shmem, migrate, move_account etc)
But, in previous trial of SwapCache handling, we saw many troubles.
Then, I'd like to go carefully step by step to handle that.

Thanks,
-Kame



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