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    SubjectRe: [PATCHv2 2/5] vmscan: Kill hibernation specific reclaim logic and unify it
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    On Tuesday 03 November 2009, Nigel Cunningham wrote:
    > Hi Rafael.
    >
    > Rafael J. Wysocki wrote:
    > > On Monday 02 November 2009, Nigel Cunningham wrote:
    > >> Hi.
    > >
    > > Hi,
    > >
    > >> KOSAKI Motohiro wrote:
    > >>>> I haven't given much thought to numa awareness in hibernate code, but I
    > >>>> can say that the shrink_all_memory interface is woefully inadequate as
    > >>>> far as zone awareness goes. Since lowmem needs to be atomically restored
    > >>>> before we can restore highmem, we really need to be able to ask for a
    > >>>> particular number of pages of a particular zone type to be freed.
    > >>> Honestly, I am not suspend/hibernation expert. Can I ask why caller need to know
    > >>> per-zone number of freed pages information? if hibernation don't need highmem.
    > >>> following incremental patch prevent highmem reclaim perfectly. Is it enough?
    > >> (Disclaimer: I don't think about highmem a lot any more, and might have
    > >> forgotten some of the details, or swsusp's algorithms might have
    > >> changed. Rafael might need to correct some of this...)
    > >>
    > >> Imagine that you have a system with 1000 pages of lowmem and 5000 pages
    > >> of highmem. Of these, 950 lowmem pages are in use and 500 highmem pages
    > >> are in use.
    > >>
    > >> In order to to be able to save an image, we need to be able to do an
    > >> atomic copy of those lowmem pages.
    > >>
    > >> You might think that we could just copy everything into the spare
    > >> highmem pages, but we can't because mapping and unmapping the highmem
    > >> pages as we copy the data will leave us with an inconsistent copy.
    > >
    > > This isn't the case any more for the mainline hibernate code. We use highmem
    > > for storing image data as well as lowmem.
    >
    > Highmem for storing copies of lowmem pages?

    It is possible in theory, but I don't think it happens in practice given the
    way in which the memory is freed. Still copy_data_page() takes this
    possibility into account.

    Thanks,
    Rafael


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