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    SubjectRe: [PATCH -v6 2/3] lib, Make gen_pool memory allocator lockless
    Hi, Peter,

    On Mon, 2010-11-29 at 20:11 +0800, Peter Zijlstra wrote:
    > On Mon, 2010-11-29 at 15:03 +0800, Huang Ying wrote:
    > > This version of the gen_pool memory allocator supports lockless
    > > operation.
    > >
    > > This makes it safe to use in NMI handlers and other special
    > > unblockable contexts that could otherwise deadlock on locks. This is
    > > implemented by using atomic operations and retries on any conflicts.
    > > The disadvantage is that there may be livelocks in extreme cases. For
    > > better scalability, one gen_pool allocator can be used for each CPU.
    > >
    > > The lockless operation only works if there is enough memory available.
    > > If new memory is added to the pool a lock has to be still taken. So
    > > any user relying on locklessness has to ensure that sufficient memory
    > > is preallocated.
    > >
    > > The basic atomic operation of this allocator is cmpxchg on long. On
    > > architectures that don't have NMI-safe cmpxchg implementation, a
    > > spin_trylock_irqsave based fallback is used for gen_pool_alloc, so it
    > > can be used in NMI handler safely. But gen_pool_free can not be used
    > > in NMI handler in these architectures, because memory free can not
    > > fail.
    > I still don't see a reason to merge this.
    > It makes the genalloc thing slower for every other user (more LOCK'ed
    > ops) and there is no new user presented in this series.

    As far as I know, all genalloc users are not performance sensitive.
    After all, it is mainly used to manage some device memory before. As for
    users, I think this is a "chicken and egg" problem. And I have plan to
    use it in APEI code.

    Best Regards,
    Huang Ying

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      Last update: 2010-11-30 02:11    [W:0.021 / U:6.644 seconds]
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