On Mon, 17 Apr 2006 10:00:02 -0700 (PDT)
Christoph Lameter <[email protected]> wrote:
> On Mon, 17 Apr 2006, KAMEZAWA Hiroyuki wrote:
>
> > > Note that there is an issue with your approach. If a migration entry is
> > > copied during fork then SWP_MIGRATION_WRITE must become SWP_MIGRATION_READ
> > > for some cases. Would you look into fixing this?
> > Thank you for pointing out the issue.
> >
> > In my understanding, copy_page_range() is used at fork().
> > This finally calls copy_one_pte() and copies ptes one by one.
>
> Right this is one spot but the ptes in the original mm must also be marked
> read. Are there any additional races?
>
Ah, yes. you are right.
> > Maybe, I'll do like this.
> > ==
> > 438 if (unlikely(!pte_present(pte)) {
> > 439 if (!pte_file(pte)) {
> > 440 swap_duplicate(pte_to_swp_entry(pte));
> > entry = pte_to_swp_entry(pte);
> > #ifdef CONFIG_MIGRATION
> > if (is_migration_entry(entry)) {
> > ......always copy as MIGRATION_READ.
> > }
> > #endif
> > 441 /* make sure dst_mm is on swapoff's mmlist. */
>
> Looks okay for this one location.
>
Then,
if (is_migration_entry(entry)) {
change_to_read_migration_entry(entry);
copy_entry(entry);
}
is sane.
-Kame
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