linux-kernel - Re: [PATCH 2/3] mm/vmscan: move RECLAIM* bits to uapi header

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Message-ID: <20200701154635.2dwwz2b6xbeyp2rc@intel.com>
Date:   Wed, 1 Jul 2020 08:46:35 -0700
From:   Ben Widawsky <ben.widawsky@...el.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        alex.shi@...ux.alibaba.com, dwagner@...e.de, tobin@...nel.org,
        cl@...ux.com, akpm@...ux-foundation.org, ying.huang@...el.com,
        dan.j.williams@...el.com, cai@....pw
Subject: Re: [PATCH 2/3] mm/vmscan: move RECLAIM* bits to uapi header

On 20-07-01 08:26:24, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> It is currently not obvious that the RECLAIM_* bits are part of the
> uapi since they are defined in vmscan.c.  Move them to a uapi header
> to make it obvious.
> 
> This should have no functional impact.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Ben Widawsky <ben.widawsky@...el.com>
> Cc: Alex Shi <alex.shi@...ux.alibaba.com>
> Cc: Daniel Wagner <dwagner@...e.de>
> Cc: "Tobin C. Harding" <tobin@...nel.org>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Qian Cai <cai@....pw>
> Cc: Daniel Wagner <dwagner@...e.de>
> 
> --
> 
> Note: This is not cc'd to stable.  It does not fix any bugs.
> ---
> 
>  b/include/uapi/linux/mempolicy.h |    7 +++++++
>  b/mm/vmscan.c                    |    8 --------
>  2 files changed, 7 insertions(+), 8 deletions(-)
> 
> diff -puN include/uapi/linux/mempolicy.h~mm-vmscan-move-RECLAIM-bits-to-uapi include/uapi/linux/mempolicy.h
> --- a/include/uapi/linux/mempolicy.h~mm-vmscan-move-RECLAIM-bits-to-uapi	2020-07-01 08:22:12.502955333 -0700
> +++ b/include/uapi/linux/mempolicy.h	2020-07-01 08:22:12.508955333 -0700
> @@ -62,5 +62,12 @@ enum {
>  #define MPOL_F_MOF	(1 << 3) /* this policy wants migrate on fault */
>  #define MPOL_F_MORON	(1 << 4) /* Migrate On protnone Reference On Node */
>  
> +/*
> + * These bit locations are exposed in the vm.zone_reclaim_mode sysctl
> + * ABI.  New bits are OK, but existing bits can never change.
> + */
> +#define RECLAIM_ZONE  (1<<0)	/* Run shrink_inactive_list on the zone */
> +#define RECLAIM_WRITE (1<<1)	/* Writeout pages during reclaim */
> +#define RECLAIM_UNMAP (1<<2)	/* Unmap pages during reclaim */

Have you considered turning this into an enum while moving it?

>  
>  #endif /* _UAPI_LINUX_MEMPOLICY_H */
> diff -puN mm/vmscan.c~mm-vmscan-move-RECLAIM-bits-to-uapi mm/vmscan.c
> --- a/mm/vmscan.c~mm-vmscan-move-RECLAIM-bits-to-uapi	2020-07-01 08:22:12.504955333 -0700
> +++ b/mm/vmscan.c	2020-07-01 08:22:12.509955333 -0700
> @@ -4091,14 +4091,6 @@ module_init(kswapd_init)
>  int node_reclaim_mode __read_mostly;
>  
>  /*
> - * These bit locations are exposed in the vm.zone_reclaim_mode sysctl
> - * ABI.  New bits are OK, but existing bits can never change.
> - */
> -#define RECLAIM_ZONE  (1<<0)	/* Run shrink_inactive_list on the zone */
> -#define RECLAIM_WRITE (1<<1)	/* Writeout pages during reclaim */
> -#define RECLAIM_UNMAP (1<<2)	/* Unmap pages during reclaim */
> -
> -/*
>   * Priority for NODE_RECLAIM. This determines the fraction of pages
>   * of a node considered for each zone_reclaim. 4 scans 1/16th of
>   * a zone.
> _