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    SubjectRe: [PATCH 2.6.13] lockless pagecache 2/7
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    From: Andi Kleen <ak@suse.de>
    Date: 02 Sep 2005 22:41:31 +0200

    > > Yeah quite a few. I suspect most MIPS also would have a problem in this
    > > area.
    >
    > cmpxchg can be done with LL/SC can't it? Any MIPS should have that.

    Right.

    On PARISC, I don't see where they are emulating compare and swap
    as indicated. They are doing the funny hashed spinlocks for the
    atomic_t operations and bitops, but that is entirely different.

    cmpxchg() has to operate in an environment where, unlike the atomic_t
    and bitops, you cannot control the accessors to the object at all.

    The DRM is the only place in the kernel that requires cmpxchg()
    and you can thus make a list of what platform can provide cmpxchg()
    by which ones support DRM and thus provide the cmpxchg() macro already
    in asm/system.h

    We really can't require support for this primitive kernel wide, it's
    simply not possible on a couple chips.
    -
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