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

From: "Huang, Ying" <ying.huang@intel.com>
To: Peter Xu <peterx@redhat.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Andrea Arcangeli <aarcange@redhat.com>,
	David Hildenbrand <david@redhat.com>,
	Minchan Kim <minchan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Nadav Amit <nadav.amit@gmail.com>,
	Hugh Dickins <hughd@google.com>,
	Andi Kleen <andi.kleen@intel.com>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v2 2/2] mm: Remember young/dirty bit for page migrations
Date: Wed, 10 Aug 2022 08:53:49 +0800	[thread overview]
Message-ID: <87wnbggbqa.fsf@yhuang6-desk2.ccr.corp.intel.com> (raw)
In-Reply-To: <YvKglA2LQkYeznZ9@xz-m1.local> (Peter Xu's message of "Tue, 9 Aug 2022 13:59:48 -0400")

Peter Xu <peterx@redhat.com> 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