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Date: Fri, 20 Apr 2018 10:17:32 -0500 (CDT)
From: Christopher Lameter <cl@linux.com>
Subject: Re: [PATCH v3 02/14] mm: Split page_type out from _mapcount
In-Reply-To: <20180418184912.2851-3-willy@infradead.org>
Message-ID: <alpine.DEB.2.20.1804201014300.18006@nuc-kabylake>
References: <20180418184912.2851-1-willy@infradead.org> <20180418184912.2851-3-willy@infradead.org>
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To: Matthew Wilcox <willy@infradead.org>
Cc: linux-mm@kvack.org, Matthew Wilcox <mawilcox@microsoft.com>, Andrew Morton <akpm@linux-foundation.org>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, Pekka Enberg <penberg@kernel.org>, Vlastimil Babka <vbabka@suse.cz>

On Wed, 18 Apr 2018, Matthew Wilcox wrote:

> As suggested by Kirill, make page_type a bitmask.  Because it starts out
> life as -1 (thanks to sharing the storage with _mapcount), 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).

Could we use bits in the page->flags for this? We could remove the node or
something else from page->flags. And the slab bit could also be part of
the page type.

The page field handling gets more and more bizarre.