Re: [PATCH v2 2/2] mm: Remember young/dirty bit for page migrations

[Huang, Ying]

Peter Xu <peterx@xxxxxxxxxx> writes:

> On Tue, Aug 09, 2022 at 04:40:12PM +0800, Huang, Ying wrote:
[snip]
>
>> I don't find pte_dirty() is synced to PageDirty() as in
>> try_to_migrate_one().  Is it a issue in the original code?
>
> I think it has?  There is:
>
> 		/* Set the dirty flag on the folio now the pte is gone. */
> 		if (pte_dirty(pteval))
> 			folio_mark_dirty(folio);
>

Sorry, my original words are confusing.  Yes, there's dirty bit syncing
in try_to_migrate_one().  But I don't find that in migrate_device.c

 $ grep dirty mm/migrate_device.c
				if (pte_soft_dirty(pte))
					swp_pte = pte_swp_mksoft_dirty(swp_pte);
				if (pte_swp_soft_dirty(pte))
					swp_pte = pte_swp_mksoft_dirty(swp_pte);
			entry = pte_mkwrite(pte_mkdirty(entry));

I guess that migrate_device.c is used to migrate between CPU visible
page to CPU un-visible page (device visible), so the rule is different?

Best Regards,
Huang, Ying