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

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Date:   Wed, 10 Aug 2022 08:53:49 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Nadav Amit <nadav.amit@...il.com>,
        Hugh Dickins <hughd@...gle.com>,
        Andi Kleen <andi.kleen@...el.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 2/2] mm: Remember young/dirty bit for page migrations

Peter Xu <peterx@...hat.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