Re: [PATCH]mmap: avoid unnecessary anon_vma lock

[Andi Kleen]

Shaohua Li <shaohua.li@xxxxxxxxx> writes:

> If we only change vma->vm_end, we can avoid taking anon_vma lock even 'insert'
> isn't NULL, which is the case of split_vma.
> From my understanding, we need the lock before because rmap must get the
> 'insert' VMA when we adjust old VMA's vm_end (the 'insert' VMA is linked to
> anon_vma list in __insert_vm_struct before).
> But now this isn't true any more. The 'insert' VMA is already linked to
> anon_vma list in __split_vma(with anon_vma_clone()) instead of
> __insert_vm_struct. There is no race rmap can't get required VMAs.
> So the anon_vma lock is unnecessary, and this can reduce one locking in brk
> case and improve scalability.

Looks good to me.
-Andi

-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only
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