Messages in this thread | | | Date | Fri, 10 Apr 2009 10:53:05 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 02/30] Remove struct mm_struct::exe_file et al |
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* Alexey Dobriyan <adobriyan@gmail.com> wrote:
> Commit 925d1c401fa6cfd0df5d2e37da8981494ccdec07 aka "procfs task > exe symlink". introduced struct mm_struct::exe_file and struct > mm_struct::num_exe_file_vmas. > > The rationale is weak: unifying MMU and no-MMU version of > /proc/*/exe code. For this a) struct mm_struct becomes bigger, b) > mmap/munmap/exit become slower, c) patch adds more code than > removes in fact.
Hm, nommu unification was not the only effect of that original patch.
The other effect was to introduce a managed 'which is the first executable vma in the mm' abstraction in struct mm. Your patch removes that abstraction and re-introduces a linear ->vma_next walk:
> + down_read(&mm->mmap_sem); > + for (vma = mm->mmap; vma; vma = vma->vm_next) { > + if ((vma->vm_flags & VM_EXECUTABLE) && vma->vm_file) {
Which can walk along thousands (or tens of thousands) of vmas until it finds the first executable vma. For example on PIE binaries it's quite possible to have a lot of non-PROT_EXEC vmas before the first EXEC vma is met.
So your revert reintroduces that linear walk. It might not matter much (/proc/*/exe might be sufficiently uninteresting in practice to not deserve an optimization), but it's still worth a mention and a discussion in the changelog.
Thanks,
Ingo
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