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

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Date:   Thu, 27 Apr 2017 15:35:23 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Igor Stoppa <igor.stoppa@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     namhyung@...nel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: Question on ___GFP_NOLOCKDEP - Was: Re: [PATCH 1/1] Remove
 hardcoding of ___GFP_xxx bitmasks

On Thu 27-04-17 15:16:47, Igor Stoppa wrote:
> 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?)

yes

> 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

Yes it should. At the time when this patch was written this value was
used. Later I've removed __GFP_OTHER by 41b6167e8f74 ("mm: get rid of
__GFP_OTHER_NODE") and forgot to refresh this one. Thanks for noticing
this.

Andrew, could you fold the following in please?
---
>From 8dc9c917af215f659bb990fa48ae7b4753027c19 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.com>
Date: Thu, 27 Apr 2017 15:28:10 +0200
Subject: [PATCH] lockdep-allow-to-disable-reclaim-lockup-detection-fix

Igor Stoppa has noticed that __GFP_NOLOCKDEP can use a lower bit. At the
time lockdep-allow-to-disable-reclaim-lockup-detection was written we
still had __GFP_OTHER_NODE but I have removed it in 41b6167e8f74 ("mm:
get rid of __GFP_OTHER_NODE") and forgot to lower the bit value.

Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 include/linux/gfp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 2b1a44f5bdb6..a89d37e8b387 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -41,7 +41,7 @@ struct vm_area_struct;
 #define ___GFP_WRITE		0x800000u
 #define ___GFP_KSWAPD_RECLAIM	0x1000000u
 #ifdef CONFIG_LOCKDEP
-#define ___GFP_NOLOCKDEP	0x4000000u
+#define ___GFP_NOLOCKDEP	0x2000000u
 #else
 #define ___GFP_NOLOCKDEP	0
 #endif
-- 
2.11.0


-- 
Michal Hocko
SUSE Labs