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Date:   Mon, 18 Feb 2019 18:42:59 +0100
From:   Vlastimil Babka <>
To:     Zi Yan <>, Matthew Wilcox <>
        Dave Hansen <>,
        Michal Hocko <>,
        "Kirill A . Shutemov" <>,
        Andrew Morton <>,
        Mel Gorman <>,
        John Hubbard <>,
        Mark Hairgrove <>,
        Nitin Gupta <>,
        David Nellans <>
Subject: Re: [RFC PATCH 01/31] mm: migrate: Add exchange_pages to exchange two
 lists of pages.

On 2/18/19 6:31 PM, Zi Yan wrote:
> The purpose of proposing exchange_pages() is to avoid allocating any new 
> page,
> so that we would not trigger any potential page reclaim or memory 
> compaction.
> Allocating a temporary page defeats the purpose.

Compaction can only happen for order > 0 temporary pages. Even if you used
single order = 0 page to gradually exchange e.g. a THP, it should be better than
u64. Allocating order = 0 should be a non-issue. If it's an issue, then the
system is in a bad state and physically contiguous layout is a secondary concern.

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