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Subject: Re: [PATCH v14 062/138] mm/migrate: Add folio_migrate_copy()
To:     Matthew Wilcox <willy@infradead.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, "Theodore Y. Ts'o" <tytso@mit.edu>
References: <20210715033704.692967-1-willy@infradead.org>
 <20210715033704.692967-63-willy@infradead.org>
 <a670e7c1-95fb-324f-055f-74dd4c81c0d0@gmail.com>
 <YPlko1ObxD/CEz8o@casper.infradead.org>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <fd3fe780-1a1b-1ba7-1725-72286470ce4c@gmail.com>
Date:   Thu, 22 Jul 2021 16:45:59 +0300
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22.07.2021 15:29, Matthew Wilcox пишет:
> On Thu, Jul 22, 2021 at 02:52:28PM +0300, Dmitry Osipenko wrote:
...
> The obvious solution is just to change folio_copy():
> 
>  {
> -       unsigned i, nr = folio_nr_pages(src);
> +       unsigned i = 0;
> +       unsigned nr = folio_nr_pages(src);
> 
> -       for (i = 0; i < nr; i++) {
> -               cond_resched();
> +       for (;;) {
>                 copy_highpage(folio_page(dst, i), folio_page(src, i));
> +               if (i++ == nr)

This works with the ++i precedence change. Thanks!

> +                       break;
> +               cond_resched();
>         }
>  }
> 
> now it only calls cond_resched() for multi-page folios.

...

Thank you for the explanation and for the fix!

The fs/ and mm/ are mostly outside of my scope, hope you'll figure out
the buffer-head case soon.