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

From: Thomas HellstrÃm (VMware)
Date: Wed Oct 09 2019 - 19:51:00 EST

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

I'd happily use that instead.