Re: [RFC] Strange do_munmap in mmap_region

[Konstantin Khlebnikov <koct9i@gmail.com>]

On Sat, Feb 28, 2015 at 9:46 AM, Wang YanQing <udknight@gmail.com> wrote:
> Hi Mel Gorman and all.
>
> I have read do_mmap_pgoff and mmap_region more than one hour,
> but still can't catch sense about below code in mmap_region:
>
> "
>         /* Clear old maps */
>         error = -ENOMEM;
> munmap_back:
>         if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) {
>                 if (do_munmap(mm, addr, len))
>                         return -ENOMEM;
>                 goto munmap_back;
>         }
> "
>
> How can we just do_munmap overlapping vma without check its vm_flags
> and new vma's vm_flags? I must miss some important things, but I can't
> figure out.
>
> You give below comment about the code in "understand the linux memory manager":)
>
> "
> If a VMA was found and it is part of the new mmapping, this removes the
>  old mmapping because the new one will cover both
> "
>
> But if new mmapping has different vm_flags or others' property, how
> can we just say the new one will cover both?
>
> I appreicate any clue and explanation about this headache question.
>
> Thanks.
>

Mmap() creates new mapping in given range
(new vma might be merged to one or both of sides if possible)
so everything what was here before is unmapped in process. Not?

>
>
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