linux-kernel - Re: [PATCH v4 2/4] mm: Split page_type out from _map

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Date:   Fri, 2 Mar 2018 11:18:06 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-mm@...ck.org, Matthew Wilcox <mawilcox@...rosoft.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        linux-kernel@...r.kernel.org,
        Fengguang Wu <fengguang.wu@...el.com>,
        linux-api@...r.kernel.org
Subject: Re: [PATCH v4 2/4] mm: Split page_type out from _map_count

On Thu, Mar 01, 2018 at 01:15:21PM -0800, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@...rosoft.com>
> 
> We're already using a union of many fields here, so stop abusing the
> _map_count and make page_type its own field.  That implies renaming some

s/_map_count/_mapcount/

and in subject.

> of the machinery that creates PageBuddy, PageBalloon and PageKmemcg;
> bring back the PG_buddy, PG_balloon and PG_kmemcg names.
> 
> As suggested by Kirill, make page_type a bitmask.  Because it starts out
> life as -1 (thanks to sharing the storage with _map_count), setting a
> page flag means clearing the appropriate bit.  This gives us space for
> probably twenty or so extra bits (depending how paranoid we want to be
> about _mapcount underflow).
> 
> Signed-off-by: Matthew Wilcox <mawilcox@...rosoft.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov