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    SubjectRe: [PATCH][0/8] (Targeting 2.6.17) Posix memory locking and balanced mlock-LRU semantic
    2006/3/21, Nick Piggin <>:
    > Stone Wang wrote:
    > > Both one of my friends(who is working on a DBMS oriented from
    > > PostgreSQL) and i had encountered unexpected OOMs with mlock/mlockall.
    > >
    > I'm not sure this is a great idea. There are more conditions than just
    > mlock that prevent pages being reclaimed. Running out of swap, for
    > example, no swap, page temporarily pinned (in other words -- any duration
    > from fleeting to permanent). I think something _much_ simpler could be
    > done for a more general approach just to teach the VM to tolerate these
    > pages a bit better.
    > Also, supposing we do want this, I think there is a fairly significant
    > queue of mm stuff you need to line up behind... it is probably asking
    > too much to target 2.6.17 for such a significant change in any case.
    > But despite all that I looked though and have a few comments ;)
    > Kudos for jumping in and getting your hands dirty! It can be tricky code.
    > > The patch brings Linux with:
    > > 1. Posix mlock/munlock/mlockall/munlockall.
    > > Get mlock/munlock/mlockall/munlockall to Posix definiton: transaction-like,
    > > just as described in the manpage(2) of mlock/munlock/mlockall/munlockall.
    > > Thus users of mlock system call series will always have an clear map of
    > > mlocked areas.
    > In what way are we not now posix compliant now?

    Currently, Linux's mlock for example, may fail with only part of its
    task finished.

    While accroding to POSIX definition:

    man mlock(2)

    On success, mlock returns zero. On error, -1 is returned, errno is set
    appropriately, and no changes are made to any locks in the address
    space of the process.

    Shaoping Wang

    > --
    > SUSE Labs, Novell Inc.
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