Re: [RFC PATCH 4/6] mm: Add COW PTE fallback function

[Chih-En Lin <shiyn.lin@gmail.com>]

On Fri, May 20, 2022 at 02:21:54PM +0000, Christophe Leroy wrote:
> > +/* COW PTE fallback to normal PTE:
> > + * - two state here
> > + *   - After break child :   [parent, rss=1, ref=1, write=NO , owner=parent]
> > + *                        to [parent, rss=1, ref=1, write=YES, owner=NULL  ]
> > + *   - After break parent:   [child , rss=0, ref=1, write=NO , owner=NULL  ]
> > + *                        to [child , rss=1, ref=1, write=YES, owner=NULL  ]
> > + */
> > +void cow_pte_fallback(struct vm_area_struct *vma, pmd_t *pmd,
> > +               unsigned long addr)
> 
> There should be a prototype in a header somewhere for a non static function.
> 
> You are encouraged to run 'make mm/memory.o C=2' to check sparse reports.
> 

I will do all the above checking before sending the next version.

> > +{
> > +       struct mm_struct *mm = vma->vm_mm;
> > +       unsigned long start, end;
> > +       pmd_t new;
> > +
> > +       BUG_ON(pmd_write(*pmd));
> 
> You seem to add a lot of BUG_ONs(). Are they really necessary ? See 
> https://docs.kernel.org/process/deprecated.html?highlight=bug_on#bug-and-bug-on
> 
> You may also use VM_BUG_ON().
> 

Sure.
I added BUG_ON() when doing the debug.
I will consider again which one is necessary.
And change to use VM_BUG_ON().

Thanks.