Re: [PATCH 1/6] mm: tracking shared dirty pages

Peter Zijlstra
2006-06-22T11:33:51Z

On Wed, 2006-06-21 at 22:56 -0700, Andrew Morton wrote:
> On Mon, 19 Jun 2006 19:52:53 +0200

> > + vma->vm_page_prot =
> > + __pgprot(pte_val
> > + (pte_wrprotect
> > + (__pte(pgprot_val(vma->vm_page_prot)))));
> > +
>
> Is there really no simpler way?

pgprot_t prot_shared = protection_map[vm_flags &
(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
pgprot_t prot_priv = protection_map[vm_flags &
(VM_READ|VM_WRITE|VM_EXEC)];

typeof(pgprot_val(prot_shared)) mask =
~(pgprot_val(prot_shared) ^ pgprot_val(prot_priv));

pgprot_val(vma->vm_page_prot) &= mask;
pgprot_val(vma->vm_page_prot) |=
(pgprot_val(prot_priv) & mask);

its more readable, but barely so.

BTW, is there a difference between:
(VM_READ|VM_WRITE|VM_EXEC)
and
(VM_READ|VM_EXEC|VM_SHARED)
in this context?

Or I can make it a generic arch specific function and override for i386
and x86-64. That way I can also cleanup drivers/char/drm/drm_vm.c where
I found this thing.

include/asm-generic/pgtable.h

#ifndef __HAVE_ARCH_PGPROT_WRPROTECT
#define pgprot_wrprotect(prot) \
({ (prot) = __pgprot(pte_val \
(pte_wrprotect \
(__pte(pgprot_val(prot))))) \
})
#endif

include/asm-{i386,x86-64}/pgtable.h

#define pgprot_wrprotect(prot) ({ pgprot_val(prot) &= ~_PAGE_RW; })
#define __HAVE_ARCH_PGPROT_WRPROTECT

I can go through some other archs and see what I can do.

Hmm, now that I look at this, might give a include-dependency problem.
Awell, thoughts, comments?