linux-kernel - Re: [PATCH] mm/page_poison: move PAGE_POISON to page

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Date:   Tue, 13 Feb 2018 11:16:15 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Wei Wang <wei.w.wang@...el.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, linux-mm@...ck.org,
        mst@...hat.com, akpm@...ux-foundation.org
Subject: Re: [PATCH] mm/page_poison: move PAGE_POISON to page_poison.c

On Fri 09-02-18 16:08:14, Wei Wang wrote:
> The PAGE_POISON macro is used in page_poison.c only, so avoid exporting
> it. Also remove the "mm/debug-pagealloc.c" related comment, which is
> obsolete.

Why is this an improvement? I thought the whole point of poison.h is to
keep all the poison value at a single place to make them obviously
unique.

> Signed-off-by: Wei Wang <wei.w.wang@...el.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> ---
>  include/linux/poison.h | 7 -------
>  mm/page_poison.c       | 6 ++++++
>  2 files changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/poison.h b/include/linux/poison.h
> index 15927eb..348bf67 100644
> --- a/include/linux/poison.h
> +++ b/include/linux/poison.h
> @@ -30,13 +30,6 @@
>   */
>  #define TIMER_ENTRY_STATIC	((void *) 0x300 + POISON_POINTER_DELTA)
>  
> -/********** mm/debug-pagealloc.c **********/
> -#ifdef CONFIG_PAGE_POISONING_ZERO
> -#define PAGE_POISON 0x00
> -#else
> -#define PAGE_POISON 0xaa
> -#endif
> -
>  /********** mm/page_alloc.c ************/
>  
>  #define TAIL_MAPPING	((void *) 0x400 + POISON_POINTER_DELTA)
> diff --git a/mm/page_poison.c b/mm/page_poison.c
> index e83fd44..8aaf076 100644
> --- a/mm/page_poison.c
> +++ b/mm/page_poison.c
> @@ -7,6 +7,12 @@
>  #include <linux/poison.h>
>  #include <linux/ratelimit.h>
>  
> +#ifdef CONFIG_PAGE_POISONING_ZERO
> +#define PAGE_POISON 0x00
> +#else
> +#define PAGE_POISON 0xaa
> +#endif
> +
>  static bool want_page_poisoning __read_mostly;
>  
>  static int early_page_poison_param(char *buf)
> -- 
> 2.7.4

-- 
Michal Hocko
SUSE Labs