Just as the swapoff system call allocates many pages of RAM to various
processes, perhaps triggering OOM, so "echo 2 >/sys/kernel/mm/ksm/run"
(unmerge) is liable to allocate many pages of RAM to various processes,
perhaps triggering OOM; and each is normally run from a modest admin
process (swapoff or shell), easily repeated until it succeeds.
So treat unmerge_and_remove_all_rmap_items() in the same way that we
treat try_to_unuse(): generalize PF_SWAPOFF to PF_OOM_ORIGIN, and
bracket both with that, to ask the OOM killer to kill them first,
to prevent them from spawning more and more OOM kills.
Signed-off-by: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
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