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From:   Huaisheng HS1 Ye <yehs1@lenovo.com>
To:     Matthew Wilcox <willy@infradead.org>
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Subject: RE: [External]  Re: [PATCH v1] include/linux/gfp.h: getting rid of
 GFP_ZONE_TABLE/BAD
Thread-Topic: [External]  Re: [PATCH v1] include/linux/gfp.h: getting rid of
 GFP_ZONE_TABLE/BAD
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Date:   Wed, 16 May 2018 12:12:00 +0000
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> From: Matthew Wilcox [mailto:willy@infradead.org]
> Sent: Saturday, May 12, 2018 10:23 PM>=20
> On Sat, May 12, 2018 at 11:35:00AM +0000, Huaisheng HS1 Ye wrote:
> > > The point of this exercise is to actually encode the zone number in
> > > the bottom bits of the GFP flags instead of something which has to be
> > > interpreted into a zone number.  When somebody sets __GFP_MOVABLE, th=
ey
> > > should also be setting ZONE_MOVABLE:
> > >
> > > -#define __GFP_MOVABLE   ((__force gfp_t)___GFP_MOVABLE)  /* ZONE_MOV=
ABLE allowed
> */
> > > +#define __GFP_MOVABLE   ((__force gfp_t)(___GFP_MOVABLE | (ZONE_MOVA=
BLE ^
> ZONE_NORMAL)))
> > >
> > I am afraid we couldn't do that, because __GFP_MOVABLE would be used po=
tentially
> with other __GFPs like __GFP_DMA and __GFP_DMA32.
>=20
> That's not a combination that makes much sense.  I know it's permitted to=
day
> (and it has the effect of being a no-op), but when you think about it, it
> doesn't actually make any sense.

Yes, you are right.
After checking almost all references of __GFP_MOVABLE and other __GFP_* fla=
gs, perhaps I was far to get excessive pursuit of logical correctness.
For those nonsense combinations, I should ignore them.
Current GFP_ZONE_TABLE can ensure all logical correctness. That makes me wa=
nt to pursue same effect.

Next, I will revise the patch according to your advice, then try to get ove=
rall testing result as far as possible.
There are many combinations because of a lot of conditions in file system a=
nd drivers. Hope I could test all things related to the lower 4 bits of gfp=
.

Sincerely,
Huaisheng Ye