linux-kernel - Re: [PATCH 1/3] mm/migrate: clean up useless code in migrate_vma_collect

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Date:   Tue, 6 Aug 2019 06:35:03 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Pingfan Liu <kernelfans@...il.com>
Cc:     linux-mm@...ck.org,
        Jérôme Glisse <jglisse@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Jan Kara <jack@...e.cz>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] mm/migrate: clean up useless code in
 migrate_vma_collect_pmd()


This needs something beyond the subject line.  Maybe ...

After these assignments, we either restart the loop with a fresh variable,
or we assign to the variable again without using the value we've assigned.

Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>

>  			goto next;
>  		}
> -		pfn = page_to_pfn(page);

After you've done all this, as far as I can tell, the 'pfn' variable is
only used in one arm of the conditions, so it can be moved there.

ie something like:

-               unsigned long mpfn, pfn;
+               unsigned long mpfn;
...
-               pfn = pte_pfn(pte);
...
+                       unsigned long pfn = pte_pfn(pte);
+