Re: [PATCH] mm: introduce for_each_vma helpers

Davidlohr Bueso
2014-08-12T23:47:00Z

On Wed, 2014-08-13 at 00:52 +0300, Kirill A. Shutemov wrote:
> On Tue, Aug 12, 2014 at 10:45:23AM -0700, Davidlohr Bueso wrote:
> > The most common way of iterating through the list of vmas, is via:
> > for (vma = mm->mmap; vma; vma = vma->vm_next)
> >
> > This patch replaces this logic with a new for_each_vma(vma) helper,
> > which 1) encapsulates this logic, and 2) make it easier to read.
>
> Why does it need to be encapsulated?
> Do you have problem with reading plain for()?
>
> Your for_each_vma(vma) assumes "mm" from the scope. This can be confusing
> for reader: whether it uses "mm" from the scope or "current->mm". This
> will lead to very hard to find bug one day.

I think its fairly obvious to see where the mm is coming from -- the
helpers *do not* necessarily use current, it uses whatever mm was
already there in the first place. I have not changed anything related to
this from the callers.

The only related change I can think of, is for some callers that do:

for (vma = current->mm->mmap; vma != NULL; vma = vma->vm_next)

So we just add a local mm from current->mm and replace the for() with
for_each_vma(). I don't see anything particularly ambiguous with that.