Messages in this thread | | | Date | Fri, 26 Sep 2008 15:54:33 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH 9/12] memcg allocate all page_cgroup at boot |
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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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