Re: [PATCH v4 3/9] mm: pagewalk: Don't split transhuge pmds when a pmd_entry is present

[Thomas HellstrÃm (VMware)]

On 10/10/19 12:30 AM, Thomas HellstrÃm (VMware) wrote:
> On 10/9/19 10:20 PM, Linus Torvalds wrote:
> > On Wed, Oct 9, 2019 at 1:06 PM Thomas HellstrÃm (VMware)
> > <thomas_os@xxxxxxxxxxxx> wrote:
> > > On 10/9/19 9:20 PM, Linus Torvalds wrote:
> > > > Don't you get it? There *is* no PTE level if you didn't split.
> > > Hmm, This paragraph makes me think we have very different 
> > > perceptions about what I'm trying to achieve.
> > It's not about what you're trying to achieve.
> >
> > It's about the actual code.
> >
> > You cannot do that
> >
> > > - split_huge_pmd(walk->vma, pmd, addr);
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ if (!ops->pmd_entry)
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ split_huge_pmd(walk->vma, pmd, addr);
> > it's insane.
> >
> > You *have* to call split_huge_pmd() if you're doing to call the
> > pte_entry() function.
> >
> > I don't understand why you are arguing. This is not about "feelings"
> > and "intentions" or about "trying to achieve".
> >
> > This is about cold hard "you can't do that", and this is now the third
> > time I tell you _why_ you can't do that: you can't walk the last level
> > if you don't _have_ a last level. You have to split the pmd to do so.
> It's not so much arguing but rather trying to understand your concerns 
> and your perception of what the final code should look like.
> > End of story.
>
> So is it that you want pte_entry() to be strictly called for *each* 
> virtual address, even if we have a pmd_entry()?
> In that case I completely follow your arguments, meaning we skip this 
> patch completely?

Or if you're still OK with your original patch

https://lore.kernel.org/lkml/CAHk-=wj5NiFPouYd6zUgY4K7VovOAxQT-xhDRjD6j5hifBWi_g@xxxxxxxxxxxxxx/

I'd happily use that instead.

Thanks,

Thomas