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From: Andi Kleen <andi@firstfloor.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: "Huang\, Ying" <ying.huang@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>, tim.c.chen@intel.com,
        dave.hansen@intel.com, andi.kleen@intel.com, aaron.lu@intel.com,
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        Hugh Dickins <hughd@google.com>, Shaohua Li <shli@kernel.org>,
        Minchan Kim <minchan@kernel.org>, Rik van Riel <riel@redhat.com>,
        Tejun Heo <tj@kernel.org>, Wu Fengguang <fengguang.wu@intel.com>
Subject: Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in swap cache
References: <1472578089-5560-1-git-send-email-ying.huang@intel.com>
        <20160831091459.GY8119@techsingularity.net>
        <87oa49m0hn.fsf@yhuang-mobile.sh.intel.com>
        <20160831153908.GA8119@techsingularity.net>
Date: Wed, 31 Aug 2016 14:35:11 -0700
In-Reply-To: <20160831153908.GA8119@techsingularity.net> (Mel Gorman's message
        of "Wed, 31 Aug 2016 16:39:08 +0100")
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Mel Gorman <mgorman@techsingularity.net> writes:
>
> __GFP_BITS_SHIFT + 5 (AS_NO_WRITEBACK_TAGS) = 31
>
> mapping->flags is a combination of AS and GFP flags so increasing
> __GFP_BITS_SHIFT overflows mapping->flags on 32-bit as gfp_t is an
> unsigned int.

Couldn't we just split mapping->flags into two fields?
I'm sure more GFP bits will be needed eventually.

-Andi