linux-kernel - Re: [PATCH] Revert "mm: remove __GFP_NO

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Date:	Tue, 20 Nov 2012 12:18:17 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Mel Gorman <mgorman@...e.de>, Zdenek Kabelac <zkabelac@...hat.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Jiri Slaby <jslaby@...e.cz>, <Valdis.Kletnieks@...edu>,
	Jiri Slaby <jirislaby@...il.com>, <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>
Subject: Re: [PATCH] Revert "mm: remove __GFP_NO_KSWAPD"

On Tue, 20 Nov 2012 13:18:19 +0400
Glauber Costa <glommer@...allels.com> wrote:

> On 11/12/2012 03:37 PM, Mel Gorman wrote:
> > diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> > index 02c1c971..d0a7967 100644
> > --- a/include/linux/gfp.h
> > +++ b/include/linux/gfp.h
> > @@ -31,6 +31,7 @@ struct vm_area_struct;
> >  #define ___GFP_THISNODE		0x40000u
> >  #define ___GFP_RECLAIMABLE	0x80000u
> >  #define ___GFP_NOTRACK		0x200000u
> > +#define ___GFP_NO_KSWAPD	0x400000u
> >  #define ___GFP_OTHER_NODE	0x800000u
> >  #define ___GFP_WRITE		0x1000000u
> 
> Keep in mind that this bit has been reused in -mm.
> If this patch needs to be reverted, we'll need to first change
> the definition of __GFP_KMEMCG (and __GFP_BITS_SHIFT as a result), or it
> would break things.

I presently have

/* Plain integer GFP bitmasks. Do not use this directly. */
#define ___GFP_DMA		0x01u
#define ___GFP_HIGHMEM		0x02u
#define ___GFP_DMA32		0x04u
#define ___GFP_MOVABLE		0x08u
#define ___GFP_WAIT		0x10u
#define ___GFP_HIGH		0x20u
#define ___GFP_IO		0x40u
#define ___GFP_FS		0x80u
#define ___GFP_COLD		0x100u
#define ___GFP_NOWARN		0x200u
#define ___GFP_REPEAT		0x400u
#define ___GFP_NOFAIL		0x800u
#define ___GFP_NORETRY		0x1000u
#define ___GFP_MEMALLOC		0x2000u
#define ___GFP_COMP		0x4000u
#define ___GFP_ZERO		0x8000u
#define ___GFP_NOMEMALLOC	0x10000u
#define ___GFP_HARDWALL		0x20000u
#define ___GFP_THISNODE		0x40000u
#define ___GFP_RECLAIMABLE	0x80000u
#define ___GFP_KMEMCG		0x100000u
#define ___GFP_NOTRACK		0x200000u
#define ___GFP_NO_KSWAPD	0x400000u
#define ___GFP_OTHER_NODE	0x800000u
#define ___GFP_WRITE		0x1000000u

and

#define __GFP_BITS_SHIFT 25	/* Room for N __GFP_FOO bits */
#define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))

Which I think is OK?

I'd forgotten about __GFP_BITS_SHIFT.  Should we do this?

--- a/include/linux/gfp.h~a
+++ a/include/linux/gfp.h
@@ -35,6 +35,7 @@ struct vm_area_struct;
 #define ___GFP_NO_KSWAPD	0x400000u
 #define ___GFP_OTHER_NODE	0x800000u
 #define ___GFP_WRITE		0x1000000u
+/* If the above are modified, __GFP_BITS_SHIFT may need updating */
 
 /*
  * GFP bitmasks..
_

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