linux-kernel - Re: [PATCH] mm : fix pte _PAGE_DIRTY bit when fallback migrate page

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Message-ID: <20200714101951.6osakxdgbhrnfrbd@box>
Date:   Tue, 14 Jul 2020 13:19:51 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Robbie Ko <robbieko@...ology.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>, linux-btrfs@...r.kernel.org,
        Roman Gushchin <guro@...com>, David Sterba <dsterba@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH] mm : fix pte _PAGE_DIRTY bit when fallback migrate page

On Tue, Jul 14, 2020 at 11:46:12AM +0200, Vlastimil Babka wrote:
> On 7/13/20 3:57 AM, Robbie Ko wrote:
> > 
> > Vlastimil Babka 於 2020/7/10 下午11:31 寫道:
> >> On 7/9/20 4:48 AM, robbieko wrote:
> >>> From: Robbie Ko <robbieko@...ology.com>
> >>>
> >>> When a migrate page occurs, we first create a migration entry
> >>> to replace the original pte, and then go to fallback_migrate_page
> >>> to execute a writeout if the migratepage is not supported.
> >>>
> >>> In the writeout, we will clear the dirty bit of the page and use
> >>> page_mkclean to clear the dirty bit along with the corresponding pte,
> >>> but page_mkclean does not support migration entry.

I don't follow the scenario.

When we establish migration entries with try_to_unmap(), it transfers
dirty bit from PTE to the page.

-- 
 Kirill A. Shutemov