Re: [PATCH 1/9] mm: Introduce new vm_insert_range API

Matthew Wilcox
2018-11-16T06:41:41Z

On Fri, Nov 16, 2018 at 11:00:30AM +0530, Souptick Joarder wrote:
> On Thu, Nov 15, 2018 at 11:44 PM Randy Dunlap <rdunlap@infradead.org> wrote:
> > On 11/15/18 7:45 AM, Souptick Joarder wrote:
> > What is the opposite of vm_insert_range() or even of vm_insert_page()?
> > or is there no need for that?
>
> There is no opposite function of vm_insert_range() / vm_insert_page().
> My understanding is, in case of any error, mmap handlers will return the
> err to user process and user space will decide the next action. So next
> time when mmap handler is getting invoked it will map from the beginning.
> Correct me if I am wrong.

The opposite function, I suppose, is unmap_region().

> > s/no./number/
>
> I didn't get it ??

This is a 'sed' expression. 's' is the 'substitute' command; the /
is a separator, 'no.' is what you wrote, and 'number' is what Randy
is recommending instead.

> > > + for (i = 0; i < page_count; i++) {
> > > + ret = vm_insert_page(vma, uaddr, pages[i]);
> > > + if (ret < 0)
> > > + return ret;
> >
> > For a non-trivial value of page_count:
> > Is it a problem if vm_insert_page() succeeds for several pages
> > and then fails?
>
> No, it will be considered as total failure and mmap handler will return
> the err to user space.

I think what Randy means is "What happens to the inserted pages?" and
the answer is that mmap_region() jumps to the 'unmap_and_free_vma'
label, which is an accurate name.

Thanks for looking, Randy.