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SubjectRe: [PATCH v6 16/24] mm: Protect mm_rb tree with a rwlock
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Hi Matthew,

Thanks for reviewing this series.

On 12/01/2018 19:48, Matthew Wilcox wrote:
> On Fri, Jan 12, 2018 at 06:26:00PM +0100, Laurent Dufour wrote:
>> -static void __vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
>> +static void __vma_rb_erase(struct vm_area_struct *vma, struct mm_struct *mm)
>> {
>> + struct rb_root *root = &mm->mm_rb;
>> /*
>> * Note rb_erase_augmented is a fairly large inline function,
>> * so make sure we instantiate it only once with our desired
>> * augmented rbtree callbacks.
>> */
>> +#ifdef CONFIG_SPF
>> + write_lock(&mm->mm_rb_lock);
>> +#endif
>> rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
>> +#ifdef CONFIG_SPF
>> + write_unlock(&mm->mm_rb_lock); /* wmb */
>> +#endif
>
> I can't say I love this. Have you considered:
>
> #ifdef CONFIG_SPF
> #define vma_rb_write_lock(mm) write_lock(&mm->mm_rb_lock)
> #define vma_rb_write_unlock(mm) write_unlock(&mm->mm_rb_lock)
> #else
> #define vma_rb_write_lock(mm) do { } while (0)
> #define vma_rb_write_unlock(mm) do { } while (0)
> #endif

I haven't consider this, but this sounds to be smarter. I'll do that.

> Also, SPF is kind of uninformative. CONFIG_MM_SPF might be better?
> Or perhaps even CONFIG_SPECULATIVE_PAGE_FAULT, just to make it really
> painful to do these one-liner ifdefs that make the code so hard to read.

Thomas also complained about that, and I agree, SPF is quite cryptic. This
being said, I don't think that CONFIG_MM_SPF will be far better, so I'll
change this define to CONFIG_SPECULATIVE_PAGE_FAULT, even if it's longer,
it should not be too much present in the code.

Thanks,
Laurent.

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