Date:   Wed, 25 Jan 2023 16:28:10 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     michel@lespinasse.org, jglisse@google.com, mhocko@suse.com,
        vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net,
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Subject: Re: [PATCH v3 2/7] mm: introduce vma->vm_flags wrapper functions
Message-Id: <20230125162810.ec222773d13cd26c55991fde@linux-foundation.org>
In-Reply-To: <20230125233554.153109-3-surenb@google.com>
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        <20230125233554.153109-3-surenb@google.com>
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On Wed, 25 Jan 2023 15:35:49 -0800 Suren Baghdasaryan <surenb@google.com> wrote:

> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -491,7 +491,15 @@ struct vm_area_struct {
>  	 * See vmf_insert_mixed_prot() for discussion.
>  	 */
>  	pgprot_t vm_page_prot;
> -	unsigned long vm_flags;		/* Flags, see mm.h. */
> +
> +	/*
> +	 * Flags, see mm.h.
> +	 * To modify use {init|reset|set|clear|mod}_vm_flags() functions.
> +	 */
> +	union {
> +		const vm_flags_t vm_flags;
> +		vm_flags_t __private __vm_flags;
> +	};

Typically when making a change like this we'll rename the affected
field/variable/function/etc.  This will reliably and deliberately break
unconverted usage sites.

This const trick will get us partway there, by breaking setters.  But
renaming it will break both setters and getters.