Re: [PATCH] mm: introduce for_each_vma helpers

Davidlohr Bueso
2014-08-12T23:30:05Z

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()?

No problem in particular. But encapsulation is always good to have, and
we have a number of examples similar to what I'm proposing all
throughout the kernel (just like at vma_interval_tree_foreach).

> 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 don't like this.
>
> > It also updates most of the callers, so its a pretty good start.
> >
> > Similarly, we also have for_each_vma_start(vma, start) when the user
> > does not want to start at the beginning of the list. And lastly the
> > for_each_vma_start_inc(vma, start, inc) helper in introduced to allow
> > users to create higher level special vma abstractions, such as with
> > the case of ELF binaries.
>
> for_each_vma_start_inc() is pretty much the plain for() but with
> really_long_and_fancy_name(). Why?

Because we can implement things like for_each_vma_gate() on top.

Thanks,
Davidlohr