Re: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages

[Aneesh Kumar K.V]

On Thursday 15 June 2017 02:18 PM, Kirill A. Shutemov wrote:
> O
> > I am not suggesting we don't do the invalidate (the need for that is
> > documented in __split_huge_pmd_locked(). I am suggesting we need a new
> > interface, something like Andrea suggested.
> >
> > old_pmd = pmdp_establish(pmd_mknotpresent());
> >
> > instead of pmdp_invalidate(). We can then use this in scenarios where we
> > want to update pmd PTE entries, where right now we go through a pmdp_clear
> > and set_pmd path. We should really not do that for THP entries.
>
> Which cases are you talking about? When do we need to clear pmd and set
> later?

With the latest upstream I am finding the usage when we mark pte clean 
page_mkclean_one . Also there is a similar usage in 
migrate_misplaced_transhuge_page(). I haven't really verified whether 
they do cause any race. But my suggestion is, we should avoid the usage 
of set_pmd_at() unless we are creating a new pmd PTE entry. If we can 
provide pmdp_establish() we can achieve that easily.

-aneesh