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    SubjectRe: [PATCH 3/3] mm: adjust rss counters for migration entiries
    KAMEZAWA Hiroyuki wrote:
    > On Fri, 06 Jan 2012 21:38:56 +0400
    > Konstantin Khlebnikov<khlebnikov@openvz.org> wrote:
    >
    >> Memory migration fill pte with migration entry and it didn't update rss counters.
    >> Then it replace migration entry with new page (or old one if migration was failed).
    >> But between this two passes this pte can be unmaped, or task can fork child and
    >> it will get copy of this migration entry. Nobody account this into rss counters.
    >>
    >> This patch properly adjust rss counters for migration entries in zap_pte_range()
    >> and copy_one_pte(). Thus we avoid extra atomic operations on migration fast-path.
    >>
    >> Signed-off-by: Konstantin Khlebnikov<khlebnikov@openvz.org>
    >
    > It's better to show wheter this is a bug-fix or not in changelog.
    >
    > IIUC, the bug-fix is the 1st harf of this patch + patch [2/3].
    > Your new bug-check code is in patch[1/3] and 2nd half of this patch.
    >

    No, there only one new bug-check in 1st patch, this is non-fatal warning.
    I didn't hide this check under CONFIG_VM_DEBUG because it rather small and
    rss counters covers whole page-table management, this is very good invariant.
    Currently I can trigger this warning only on this rare race -- extremely loaded
    memory compaction catches this every several seconds.

    1/3 bug-check
    2/3 fix preparation
    3/3 bugfix in two places:
    do rss++ in copy_one_pte()
    do rss-- in zap_pte_range()

    > I think it's better to do bug-fix 1st and add bug-check later.
    >
    > So, could you reorder patches to bug-fix and new-bug-check ?

    Patches didn't share any context, so they can be applied in any order.

    >
    > To the logic itself,
    > Acked-by: KAMEZAWA Hiroyuki<kamezawa.hiroyu@jp.fujitsu.com>
    > Please CC when you repost.
    >
    >
    >




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