On Wed, Feb 15, 2023 at 09:17:41PM -0800, Suren Baghdasaryan wrote: > When vma->anon_vma is not set, page fault handler will set it by either > reusing anon_vma of an adjacent VMA if VMAs are compatible or by > allocating a new one. find_mergeable_anon_vma() walks VMA tree to find > a compatible adjacent VMA and that requires not only the faulting VMA > to be stable but also the tree structure and other VMAs inside that tree. > Therefore locking just the faulting VMA is not enough for this search. > Fall back to taking mmap_lock when vma->anon_vma is not set. This > situation happens only on the first page fault and should not affect > overall performance. I think I asked this before, but don't remember getting an aswer. Why do we defer setting anon_vma to the first fault? Why don't we set it up at mmap time?
