Re: [RFC PATCH 00/12] x86/mm: Implement lockless pgd_alloc()/pgd_free()

[Ingo Molnar]

[ I fat-fingered the linux-mm Cc:, so every reply will bounce on that,
  sorry about that  :-/ Fixed it in this mail's Cc: list. ]

* Ingo Molnar <mingo@xxxxxxxxxx> wrote:

> Waiman Long reported 'pgd_lock' contention on high CPU count systems and 
> proposed moving pgd_lock on a separate cacheline to eliminate false sharing and 
> to reduce some of the lock bouncing overhead.

So 'pgd_lock' is a global lock, used for every new task creation:

arch/x86/mm/fault.c:DEFINE_SPINLOCK(pgd_lock);

which with a sufficiently high CPU count starts to hurt.

Thanks,

	Ingo
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