linux-kernel - RE: [External] Re: [PATCH v1] include/linux/gfp.h: getting rid of GFP_ZONE

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Message-ID: <HK2PR03MB1684A881A868E9676C7E55E692920@HK2PR03MB1684.apcprd03.prod.outlook.com>
Date:   Wed, 16 May 2018 12:12:00 +0000
From:   Huaisheng HS1 Ye <yehs1@...ovo.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "mhocko@...e.com" <mhocko@...e.com>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "alexander.levin@...izon.com" <alexander.levin@...izon.com>,
        "colyli@...e.de" <colyli@...e.de>,
        NingTing Cheng <chengnt@...ovo.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [External]  Re: [PATCH v1] include/linux/gfp.h: getting rid of
 GFP_ZONE_TABLE/BAD

> From: Matthew Wilcox [mailto:willy@...radead.org]
> Sent: Saturday, May 12, 2018 10:23 PM> 
> 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, they
> > > should also be setting ZONE_MOVABLE:
> > >
> > > -#define __GFP_MOVABLE   ((__force gfp_t)___GFP_MOVABLE)  /* ZONE_MOVABLE allowed
> */
> > > +#define __GFP_MOVABLE   ((__force gfp_t)(___GFP_MOVABLE | (ZONE_MOVABLE ^
> ZONE_NORMAL)))
> > >
> > I am afraid we couldn't do that, because __GFP_MOVABLE would be used potentially
> with other __GFPs like __GFP_DMA and __GFP_DMA32.
> 
> That's not a combination that makes much sense.  I know it's permitted today
> (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_* flags, 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 want to pursue same effect.

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

Sincerely,
Huaisheng Ye