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Re: [lkp-robot] [x86/mm] 9e52fc2b50: will-it-scale.per_thread_ops -16% regression

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On Fri, Sep 29, 2017 at 02:24:03PM +0200, Vitaly Kuznetsov wrote:
> 1) In case the system is under extreme memory pressure and
> __get_free_page() is failing in tlb_remove_table() we'll be doing
> smp_call_function() for _each_ call (avoiding batching). We may want to
> have a pre-allocated pool.

MMU_GATHER_BUNDLE should avoid it being for _every_ call.

Also, note that tlb_gather is preemptible, so pre-alloc is 'difficult'
and you will run out, esp. when memory is right.

> 2) The default MAX_TABLE_BATCH is static (it is equal to the number of
> pointer we can fit into one page - sizeof(struct mmu_table_batch) ==
> 509), we may want to adjust it for very big systems.

That would then put more stress on the memory allocator because you're
then asking for higher order pages.

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Re: [lkp-robot] [x86/mm]  9e52fc2b50:  will-it-scale.per_thread_ops -16% regression Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-09-29 14:30 +0200
  Re: [lkp-robot] [x86/mm]  9e52fc2b50:  will-it-scale.per_thread_ops  -16% regression Peter Zijlstra <peterz@infradead.org> - 2017-09-29 15:20 +0200
    Re: [lkp-robot] [x86/mm]  9e52fc2b50:  will-it-scale.per_thread_ops  -16% regression Peter Zijlstra <peterz@infradead.org> - 2017-09-29 15:20 +0200
      Re: [lkp-robot] [x86/mm]  9e52fc2b50:  will-it-scale.per_thread_ops -16% regression Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-09-29 16:10 +0200

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