linux-kernel - Question on ___GFP_NOLOCKDEP - Was: Re: [PATCH 1/1] Remove hardcoding of ___GFP

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Date:   Thu, 27 Apr 2017 15:18:58 +0300
From:   Igor Stoppa <igor.stoppa@...wei.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     <namhyung@...nel.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Question on ___GFP_NOLOCKDEP - Was: Re: [PATCH 1/1] Remove hardcoding
 of ___GFP_xxx bitmasks

On 26/04/17 18:29, Igor Stoppa wrote:

> On 26/04/17 17:47, Michal Hocko wrote:

[...]

>> Also the current mm tree has ___GFP_NOLOCKDEP which is not addressed
>> here so I suspect you have based your change on the Linus tree.

> I used your tree from kernel.org

I found it, I was using master, instead of auto-latest (is it correct?)
But now I see something that I do not understand (apologies if I'm
asking something obvious).

First there is:

[...]
#define ___GFP_WRITE		0x800000u
#define ___GFP_KSWAPD_RECLAIM	0x1000000u
#ifdef CONFIG_LOCKDEP
#define ___GFP_NOLOCKDEP	0x4000000u
#else
#define ___GFP_NOLOCKDEP	0
#endif

Then:

/* Room for N __GFP_FOO bits */
#define __GFP_BITS_SHIFT (25 + IS_ENABLED(CONFIG_LOCKDEP))



Shouldn't it be either:
___GFP_NOLOCKDEP	0x2000000u

or:

#define __GFP_BITS_SHIFT (25 + 2 * IS_ENABLED(CONFIG_LOCKDEP))


thanks, igor