On Thu, 15 Nov 2012, Kirill A. Shutemov wrote: > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > > index d767a7c..05490b3 100644 > > > --- a/mm/huge_memory.c > > > +++ b/mm/huge_memory.c > > > @@ -1259,6 +1259,8 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > > pmd_t entry; > > > entry = pmdp_get_and_clear(mm, addr, pmd); > > > entry = pmd_modify(entry, newprot); > > > + if (is_huge_zero_pmd(entry)) > > > + entry = pmd_wrprotect(entry); > > > set_pmd_at(mm, addr, pmd, entry); > > > spin_unlock(&vma->vm_mm->page_table_lock); > > > ret = 1; > > > > Nack, this should be handled in pmd_modify(). > > I disagree. It means we will have to enable hzp per arch. Bad idea. > pmd_modify() only exists for those architectures with thp support already, so you've already implicitly enabled for all the necessary architectures with your patchset. > What's wrong with the check? > Anybody using pmd_modify() to set new protections in the future perhaps without knowledge of huge zero page can incorrectly make the huge zero page writable, which can never be allowed to happen. It's better to make sure it can never happen with the usual interface to modify protections. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>