linux-kernel - Re: [PATCH] mm: introduce pmd|pte_need_soft_dirty

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Date: Fri, 7 Jun 2024 21:00:38 +1200
From: Barry Song <21cnbao@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org, chrisl@...nel.org, 
	kasong@...cent.com, linux-kernel@...r.kernel.org, minchan@...nel.org, 
	ryan.roberts@....com, surenb@...gle.com, v-songbaohua@...o.com, 
	willy@...radead.org
Subject: Re: [PATCH] mm: introduce pmd|pte_need_soft_dirty_wp helpers for
 softdirty write-protect

On Fri, Jun 7, 2024 at 8:46 PM David Hildenbrand <david@...hat.com> wrote:
>
> On 06.06.24 05:40, Barry Song wrote:
> > From: Barry Song <v-songbaohua@...o.com>
> >
> > This patch introduces the pte_need_soft_dirty_wp and
> > pmd_need_soft_dirty_wp helpers to determine if write protection is
> > required for softdirty tracking. This can enhance code readability
> > and improve its overall appearance.
> >
> > These new helpers are utilized in gup, huge_memory, and protect,
> > and are particularly applied in do_swap_page() to optimize a
> > softdirty scenario where mkwrite can still be performed.
>
> [...]
>
> > +static inline bool pmd_need_soft_dirty_wp(struct vm_area_struct *vma, pmd_t pmd)
> > +{
> > +     return vma_soft_dirty_enabled(vma) && !pmd_soft_dirty(pmd);
> > +}
> > +
> > +static inline bool pte_need_soft_dirty_wp(struct vm_area_struct *vma, pte_t pte)
> > +{
> > +     return vma_soft_dirty_enabled(vma) && !pte_soft_dirty(pte);
> > +}
> > +
>
> Should these be "needs" ? I tend to like these names/semantics.

yes. "needs" is better. Glad to know you have the common liking
for these names.

>
>
> >   static inline void vma_iter_config(struct vma_iterator *vmi,
> >               unsigned long index, unsigned long last)
> >   {
> > diff --git a/mm/memory.c b/mm/memory.c
> > index db9130488231..6307c43796aa 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -4322,7 +4322,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> >       if (!folio_test_ksm(folio) &&
> >           (exclusive || folio_ref_count(folio) == 1)) {
> >               if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
> > -                 !vma_soft_dirty_enabled(vma)) {
> > +                 !pte_need_soft_dirty_wp(vma, pte)) {
> >                       pte = pte_mkwrite(pte, vma);
>
> I would move that into a separate patch, as it's not a simple conversion.
>

cool. will separate it in v2.

> --
> Cheers,
>
> David / dhildenb
>

Thanks
Barry