Re: [PATCH 5/5] Swapless V2: Revise main migration logic

[KAMEZAWA Hiroyuki]

On Mon, 17 Apr 2006 10:00:02 -0700 (PDT)
Christoph Lameter <clameter@xxxxxxx> 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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