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    mm: numa: define _PAGE_NUMA · dbe4d203
    Andrea Arcangeli 提交于
    The objective of _PAGE_NUMA is to be able to trigger NUMA hinting page
    faults to identify the per NUMA node working set of the thread at
    runtime.
    
    Arming the NUMA hinting page fault mechanism works similarly to
    setting up a mprotect(PROT_NONE) virtual range: the present bit is
    cleared at the same time that _PAGE_NUMA is set, so when the fault
    triggers we can identify it as a NUMA hinting page fault.
    
    _PAGE_NUMA on x86 shares the same bit number of _PAGE_PROTNONE (but it
    could also use a different bitflag, it's up to the architecture to
    decide).
    
    It would be confusing to call the "NUMA hinting page faults" as
    "do_prot_none faults". They're different events and _PAGE_NUMA doesn't
    alter the semantics of mprotect(PROT_NONE) in any way.
    
    Sharing the same bitflag with _PAGE_PROTNONE in fact complicates
    things: it requires us to ensure the code paths executed by
    _PAGE_PROTNONE remains mutually exclusive to the code paths executed
    by _PAGE_NUMA at all times, to avoid _PAGE_NUMA and _PAGE_PROTNONE to
    step into each other toes.
    
    Because we want to be able to set this bitflag in any established pte
    or pmd (while clearing the present bit at the same time) without
    losing information, this bitflag must never be set when the pte and
    pmd are present, so the bitflag picked for _PAGE_NUMA usage, must not
    be used by the swap entry format.
    Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
    Signed-off-by: NMel Gorman <mgorman@suse.de>
    Reviewed-by: NRik van Riel <riel@redhat.com>
    dbe4d203
pgtable_types.h 11.7 KB