Messages in this thread | | | Date | Wed, 19 Apr 2006 09:50:44 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: Read/Write migration entries: Implement correct behavior in copy_one_pte |
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On Tue, 18 Apr 2006 11:21:25 -0700 (PDT) Christoph Lameter <clameter@sgi.com> wrote:
> Note that this is again only a partial solution. mprotect() also has the > potential of changing the write status to read. yes. in change_pte_range().
Note: fork() and mprotect() both requires mm->mmap_sem. So both of them is not problem when migration holds mm->mmap_sem. If we does lazy migration or memory hot removing or allows migration from another process, this will be problem.
> Are there any additional occurrences? Would you check and fix this one as well? > pte_modify() looks to be called only by mprotect(). I checked all mk_pte() but not found no occurrences now. But I'll have to do more.
> If we cannot get to all the locations or if these fixes get too extensive > then I think we better drop the preservation of write permissions and > tolerate the occurrence of some useless COW after migration. > yes. I agree.
-Kame > > > Migration entries with write permission must become SWP_MIGRATION_READ > entries if a COW mapping is processed. The migration entries from which > the copy is being made must also become SWP_MIGRATION_READ. This mimicks > the copying of pte for an anonymous page. > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > Signed-off-by: Christoph Lameter <clameter@sgi.com> > > Index: linux-2.6.17-rc1-mm3/mm/memory.c > =================================================================== > --- linux-2.6.17-rc1-mm3.orig/mm/memory.c 2006-04-18 10:58:33.000000000 -0700 > +++ linux-2.6.17-rc1-mm3/mm/memory.c 2006-04-18 11:09:23.000000000 -0700 > @@ -434,7 +434,9 @@ copy_one_pte(struct mm_struct *dst_mm, s > /* pte contains position in swap or file, so copy. */ > if (unlikely(!pte_present(pte))) { > if (!pte_file(pte)) { > - swap_duplicate(pte_to_swp_entry(pte)); > + swp_entry_t entry = pte_to_swp_entry(pte); > + > + swap_duplicate(entry); > /* make sure dst_mm is on swapoff's mmlist. */ > if (unlikely(list_empty(&dst_mm->mmlist))) { > spin_lock(&mmlist_lock); > @@ -443,6 +445,19 @@ copy_one_pte(struct mm_struct *dst_mm, s > &src_mm->mmlist); > spin_unlock(&mmlist_lock); > } > + if (is_migration_entry(entry) && > + is_cow_mapping(vm_flags)) { > + page = migration_entry_to_page(entry); > + > + /* > + * COW mappings require pages in both parent > + * and child to be set to read. > + */ > + entry = make_migration_entry(page, > + ` SWP_MIGRATION_READ); > + pte = swp_entry_to_pte(entry); > + set_pte_at(src_mm, addr, src_pte, pte); > + } > } > goto out_set_pte; > } >
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