On Mon, 2016-09-26 at 10:46 +0200, Michal Hocko wrote:
> On Fri 23-09-16 17:53:51, Oleg Nesterov wrote:
> > On 09/23, Michal Hocko wrote:
> > >
> > > On Fri 23-09-16 15:56:36, Oleg Nesterov wrote:
> > > >
> > > > I think we can simplify this patch. And imo make it better. How about
> > >
> > > it is certainly less subtle because it doesn't report "sub-vmas".
> > >
> > > > if (last_addr) {
> > > > vma = find_vma(mm, last_addr - 1);
> > > > if (vma && vma->vm_start <= last_addr)
> > > > vma = m_next_vma(priv, vma);
> > > > if (vma)
> > > > return vma;
> > > > }
> > >
> > > we would still miss a VMA if the last one got shrunk/split
> >
> > Not sure I understand what you mean... If the last one was split
> > we probably should not report the new vma.
>
> Right, VMA split is less of a problem. I meant to say that if the
> last_vma->vm_end got lower for whatever reason then we could miss a VMA
> right after. We actually might want to display such a VMA because it
> could be a completely new one. We just do not know whether it is a
> former split with enlarged VMA or a completely new one
>
> [ old VMA ] Hole [ VMA ]
> [ old VMA ][ New VMa ] [ VMA ]
This is indeed possible. But I see this is like the last_vma enlargement
case. I suggest we accept such missing, as we accept the enlargement
part of last_vma is not printed.
How about we set such target: 1) no duplicate print; 2) no old vma
missing (unless it's unmapped); 3) monotonic printing.
We accept those newly added/changed parts between 2 partial reads is not
printed.
How about above suggestion? If you, Dave, Oleg and others accept it,
then Oleg's improvement can achieve it, I think.
>
> > Nevermind, in any case yes, sure, this can't "fix" other corner cases.
>
> Agreed, or at least I do not see an easy way for that.
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