linux-kernel - Re: [External] Re: [PATCH 2/3] include/linux/gfp.h: use unsigned int in gfp

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Date:   Sun, 6 May 2018 06:48:14 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Huaisheng HS1 Ye <yehs1@...ovo.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "pasha.tatashin@...cle.com" <pasha.tatashin@...cle.com>,
        "alexander.levin@...izon.com" <alexander.levin@...izon.com>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "penguin-kernel@...ove.SAKURA.ne.jp" 
        <penguin-kernel@...ove.SAKURA.ne.jp>,
        "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 2/3] include/linux/gfp.h: use unsigned
 int in gfp_zone

On Sun, May 06, 2018 at 09:32:15AM +0000, Huaisheng HS1 Ye wrote:
> This idea is great, we can replace GFP_ZONE_TABLE and GFP_ZONE_BAD with it.
> I have realized it preliminarily based on your code and tested it on a 2 sockets platform. Fortunately, we got a positive test result.

Great!

> I made some adjustments for __GFP_HIGHMEM, this flag is special than others, because the return result of gfp_zone has two possibilities, which depend on ___GFP_MOVABLE has been enabled or disabled.
> When ___GFP_MOVABLE has been enabled, ZONE_MOVABLE shall be returned. When disabled, OPT_ZONE_HIGHMEM shall be used.
> 
> #define __GFP_DMA	((__force gfp_t)OPT_ZONE_DMA ^ ZONE_NORMAL)
> #define __GFP_HIGHMEM	((__force gfp_t)ZONE_MOVABLE ^ ZONE_NORMAL)

I'm not sure this is right ... Let me think about this a little.

> #define __GFP_DMA32	((__force gfp_t)OPT_ZONE_DMA32 ^ ZONE_NORMAL)
> #define __GFP_MOVABLE	((__force gfp_t)___GFP_MOVABLE)  /* ZONE_MOVABLE allowed */
> #define GFP_ZONEMASK	((__force gfp_t)___GFP_ZONE_MASK | ___GFP_MOVABLE)
> 
> The present situation is that, based on this change, the bits of flags, __GFP_DMA and __GFP_HIGHMEM and __GFP_DMA32, have been encoded.
> That is totally different from existing code, you know in kernel scope, there are many drivers or subsystems use these flags directly to realize bit manipulations like this below,
> swiotlb-xen.c (drivers\xen):	flags &= ~(__GFP_DMA | __GFP_HIGHMEM);
> extent_io.c (fs\btrfs):			mask &= ~(__GFP_DMA32|__GFP_HIGHMEM);
> 
> Because of these flags have been encoded, the above operations can cause problem.
> I am trying to get a solution to resolve it. Any progress will be reported.

These users probably want:

flags &= GFP_RECLAIM_MASK;