Shaohua Li <shaohua.li@xxxxxxxxx> writes:
> Avoid merging a VMA with another VMA which is cloned from parent process. The
> cloned VMA shares lock with parent process's VMA. If we do the merge, more vma
> area (even the new range is only for current process) uses perent process's
> anon_vma lock, so introduces scalability issues.
> find_mergeable_anon_vma already considers this.
In theory this could prevent quite some VMA merging, but I guess the
tradeoff is worth it and that should be unlikely to hit anyways.
> static inline int is_mergeable_anon_vma(struct anon_vma *anon_vma1,
> - struct anon_vma *anon_vma2)
> + struct anon_vma *anon_vma2,
> + struct vm_area_struct *vma)
> {
> - return !anon_vma1 || !anon_vma2 || (anon_vma1 == anon_vma2);
> + if ((!anon_vma1 || !anon_vma2) && (!vma ||
> + list_is_singular(&vma->anon_vma_chain)))
> + return 1;
I think this if () needs a comment.
-Andi
--
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