Re: [PATCH v2 07/19] mm/fork: Accept huge pfnmap entries

[Andrew Morton]

On Mon, 9 Sep 2024 18:43:22 -0400 Peter Xu <peterx@xxxxxxxxxx> wrote:

> > > > Do we need the logic to clear dirty bit in the child as that in
> > > > __copy_present_ptes()?  (and also for the pmd's case).
> > > > 
> > > > e.g.
> > > > if (vma->vm_flags & VM_SHARED)
> > > > 	pud = pud_mkclean(pud);
> > > 
> > > Yeah, good question.  I remember I thought about that when initially
> > > working on these lines, but I forgot the details, or maybe I simply tried
> > > to stick with the current code base, as the dirty bit used to be kept even
> > > in the child here.
> > > 
> > > I'd expect there's only performance differences, but still sounds like I'd
> > > better leave that to whoever knows the best on the implications, then draft
> > > it as a separate patch but only when needed.
> > 
> > Sorry, but this vaguensss simply leaves me with nowhere to go.
> > 
> > I'll drop the series - let's revisit after -rc1 please.
> 
> Andrew, would you please explain why it needs to be dropped?
> 
> I meant in the reply that I think we should leave that as is, and I think
> so far nobody in real life should care much on this bit, so I think it's
> fine to leave the dirty bit as-is.
> 
> I still think whoever has a better use of the dirty bit and would like to
> change the behavior should find the use case and work on top, but only if
> necessary.

Well.  "I'd expect there's only performance differences" means to me
"there might be correctness issues, I don't know".  Is it or is it not
merely a performance thing?