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    SubjectRe: [PATCH V5 5/7] mm: mmap: Add mmap flag to request VM_LOCKONFAULT
    On Mon, 27 Jul 2015, Kirill A. Shutemov wrote:

    > On Fri, Jul 24, 2015 at 05:28:43PM -0400, Eric B Munson wrote:
    > > The cost of faulting in all memory to be locked can be very high when
    > > working with large mappings. If only portions of the mapping will be
    > > used this can incur a high penalty for locking.
    > >
    > > Now that we have the new VMA flag for the locked but not present state,
    > > expose it as an mmap option like MAP_LOCKED -> VM_LOCKED.
    >
    > As I mentioned before, I don't think this interface is justified.
    >
    > MAP_LOCKED has known issues[1]. The MAP_LOCKED problem is not necessary
    > affects MAP_LOCKONFAULT, but still.
    >
    > Let's not add new interface unless it's demonstrably useful.
    >
    > [1] http://lkml.kernel.org/g/20150114095019.GC4706@dhcp22.suse.cz

    I understand and should have been more explicit. This patch is still
    included becuase I have an internal user that wants to see it added.
    The problem discussed in the thread you point out does not affect
    MAP_LOCKONFAULT because we do not attempt to populate the region with
    MAP_LOCKONFAULT.

    As I told Vlastimil, if this is a hard NAK with the patch I can work
    with that. Otherwise I prefer it stays.

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