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From: Huaisheng HS1 Ye <yehs1@lenovo.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"mhocko@suse.com" <mhocko@suse.com>,
	"vbabka@suse.cz" <vbabka@suse.cz>,
	"mgorman@techsingularity.net" <mgorman@techsingularity.net>,
	"alexander.levin@verizon.com" <alexander.levin@verizon.com>,
	"colyli@suse.de" <colyli@suse.de>,
	NingTing Cheng <chengnt@lenovo.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [External]  Re: [PATCH v1] include/linux/gfp.h: getting rid of GFP_ZONE_TABLE/BAD
Date: Fri, 11 May 2018 03:24:34 +0000	[thread overview]
Message-ID: <HK2PR03MB16843E14AD56B3E546D9F52D929F0@HK2PR03MB1684.apcprd03.prod.outlook.com> (raw)
In-Reply-To: <20180510163023.GB30442@bombadil.infradead.org>

> From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] On Behalf Of Matthew
> Wilcox
> On Fri, May 11, 2018 at 12:10:25AM +0800, Huaisheng Ye wrote:
> > -#define __GFP_DMA	((__force gfp_t)___GFP_DMA)
> > -#define __GFP_HIGHMEM	((__force gfp_t)___GFP_HIGHMEM)
> > -#define __GFP_DMA32	((__force gfp_t)___GFP_DMA32)
> > +#define __GFP_DMA	((__force gfp_t)OPT_ZONE_DMA ^ ZONE_NORMAL)
> > +#define __GFP_HIGHMEM	((__force gfp_t)ZONE_MOVABLE ^ ZONE_NORMAL)
> > +#define __GFP_DMA32	((__force gfp_t)OPT_ZONE_DMA32 ^ ZONE_NORMAL)
> 
> No, you've made gfp_zone even more complex than it already is.
> If you can't use OPT_ZONE_HIGHMEM here, then this is a waste of time.
> 
Dear Matthew,

The reason why I don't use OPT_ZONE_HIGHMEM for __GFP_HIGHMEM	 directly is that, for x86_64 platform there is no CONFIG_HIGHMEM, so OPT_ZONE_HIGHMEM shall always be equal to ZONE_NORMAL.

For gfp_zone it is impossible to distinguish the meaning of lowest 3 bits in flags. How can gfp_zone to understand it comes from OPT_ZONE_HIGHMEM or ZONE_NORMAL?
And the most pained thing is that, if __GFP_HIGHMEM with movable flag enabled, it means that ZONE_MOVABLE shall be returned.
That is different from ZONE_DMA, ZONE_DMA32 and ZONE_NORMAL.

I was thinking...
Whether it is possible to use other judgement condition to decide OPT_ZONE_HIGHMEM or ZONE_MOVABLE shall be returned from gfp_zone.

Sincerely,
Huaisheng Ye


> >  static inline enum zone_type gfp_zone(gfp_t flags)
> >  {
> >  	enum zone_type z;
> > -	int bit = (__force int) (flags & GFP_ZONEMASK);
> > +	z = ((__force unsigned int)flags & ___GFP_ZONE_MASK) ^ ZONE_NORMAL;
> > +
> > +	if (z > OPT_ZONE_HIGHMEM)
> > +		z = OPT_ZONE_HIGHMEM +
> > +			!!((__force unsigned int)flags & ___GFP_MOVABLE);
> >
> > -	z = (GFP_ZONE_TABLE >> (bit * GFP_ZONES_SHIFT)) &
> > -					 ((1 << GFP_ZONES_SHIFT) - 1);
> > -	VM_BUG_ON((GFP_ZONE_BAD >> bit) & 1);
> > +	VM_BUG_ON(z > ZONE_MOVABLE);
> >  	return z;
> >  }

  reply	other threads:[~2018-05-11  3:24 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1525968625-40825-1-git-send-email-yehs1@lenovo.com>
2018-05-10 16:30 ` Matthew Wilcox
2018-05-11  3:24   ` Huaisheng HS1 Ye [this message]
2018-05-11 13:26     ` [External] " Matthew Wilcox
2018-05-12 11:35       ` Huaisheng HS1 Ye
2018-05-12 14:22         ` Matthew Wilcox
2018-05-16 12:12           ` Huaisheng HS1 Ye
2018-05-18  3:03       ` Huaisheng HS1 Ye

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