linux-kernel - Re: [PATCH v3 2/2] mm: redefine VM

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Message-ID: <20251002080304.GA26368@dev-dsk-acsjakub-1b-6f9934e2.eu-west-1.amazon.com>
Date: Thu, 2 Oct 2025 08:03:04 +0000
From: Jakub Acs <acsjakub@...zon.de>
To: David Hildenbrand <david@...hat.com>
CC: <linux-mm@...ck.org>, <akpm@...ux-foundation.org>, <xu.xin16@....com.cn>,
	<chengming.zhou@...ux.dev>, <peterx@...hat.com>, <axelrasmussen@...gle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] mm: redefine VM_* flag constants with BIT()

On Wed, Oct 01, 2025 at 04:04:51PM +0200, David Hildenbrand wrote:
> >-#define VM_GROWSDOWN	0x00000100	/* general info on the segment */
> >+#define VM_GROWSDOWN	BIT(8)		/* general info on the segment */
> >  #ifdef CONFIG_MMU
> >-#define VM_UFFD_MISSING	0x00000200	/* missing pages tracking */
> >+#define VM_UFFD_MISSING	BIT(9)		/* missing pages tracking */
> >  #else /* CONFIG_MMU */
> >-#define VM_MAYOVERLAY	0x00000200	/* nommu: R/O MAP_PRIVATE mapping that might overlay a file mapping */
> >+#define VM_MAYOVERLAY	BIT(10)		/* nommu: R/O MAP_PRIVATE mapping that might overlay a file mapping */
> 
> Careful: VM_UFFD_MISSING and VM_MAYOVERLAY share the same bit,
> depending on CONFIG_MMU (9).
> 
> >  #define VM_UFFD_MISSING	0
> >  #endif /* CONFIG_MMU */
> >-#define VM_PFNMAP	0x00000400	/* Page-ranges managed without "struct page", just pure PFN */
> >-#define VM_UFFD_WP	0x00001000	/* wrprotect pages tracking */
> >+#define VM_PFNMAP	BIT(11)		/* Page-ranges managed without "struct page", just pure PFN */
> 
> -> 10

Ugh, thanks for catching these!

> 
> 11 is actually unused IIUC.
> 
> >+#define VM_UFFD_WP	BIT(12)		/* wrprotect pages tracking */
> 
> This seems to be correct again.
> 
> 
> IIRC, Andrew prefers not mixing fixes and cleanups in the same
> series if possible. So you might just want to send out patch #1
> separately and, send out patch #2 separately with a note under the
> --- that it depends on patch #1.
> 

I saw that patch #1 was applied so will leave that alone now, but took a
note for future.

For completeness adding the link to v4:
https://lore.kernel.org/all/20251002075202.11306-1-acsjakub@amazon.de/

Many Thanks,
Jakub



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