linux-kernel - Re: [PATCH v5 1/6] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE

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Message-Id: <87sht0y1rq.fsf@linux.vnet.ibm.com>
Date:   Fri, 16 Sep 2016 08:44:17 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     js1304@...il.com, Andrew Morton <akpm@...ux-foundation.org>
Cc:     Rik van Riel <riel@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        mgorman@...hsingularity.net, Laura Abbott <lauraa@...eaurora.org>,
        Minchan Kim <minchan@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Michal Nazarewicz <mina86@...a86.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v5 1/6] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request

js1304@...il.com writes:

> From: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> Freepage on ZONE_HIGHMEM doesn't work for kernel memory so it's not that
> important to reserve. When ZONE_MOVABLE is used, this problem would
> theorectically cause to decrease usable memory for GFP_HIGHUSER_MOVABLE
> allocation request which is mainly used for page cache and anon page
> allocation. So, fix it.
>
> And, defining sysctl_lowmem_reserve_ratio array by MAX_NR_ZONES - 1 size
> makes code complex. For example, if there is highmem system, following
> reserve ratio is activated for *NORMAL ZONE* which would be easyily
> misleading people.
>
>  #ifdef CONFIG_HIGHMEM
>  32
>  #endif
>
> This patch also fix this situation by defining sysctl_lowmem_reserve_ratio
> array by MAX_NR_ZONES and place "#ifdef" to right place.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> ---
>  include/linux/mmzone.h | 2 +-
>  mm/page_alloc.c        | 7 ++++---
>  2 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index d572b78..e3f39af 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -877,7 +877,7 @@ int min_free_kbytes_sysctl_handler(struct ctl_table *, int,
>  					void __user *, size_t *, loff_t *);
>  int watermark_scale_factor_sysctl_handler(struct ctl_table *, int,
>  					void __user *, size_t *, loff_t *);
> -extern int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1];
> +extern int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES];
>  int lowmem_reserve_ratio_sysctl_handler(struct ctl_table *, int,
>  					void __user *, size_t *, loff_t *);
>  int percpu_pagelist_fraction_sysctl_handler(struct ctl_table *, int,
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4f7d5d7..a8310de 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -198,17 +198,18 @@ static void __free_pages_ok(struct page *page, unsigned int order);
>   * TBD: should special case ZONE_DMA32 machines here - in those we normally
>   * don't need any ZONE_NORMAL reservation
>   */
> -int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1] = {
> +int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES] = {
>  #ifdef CONFIG_ZONE_DMA
>  	 256,
>  #endif
>  #ifdef CONFIG_ZONE_DMA32
>  	 256,
>  #endif
> -#ifdef CONFIG_HIGHMEM
>  	 32,
> +#ifdef CONFIG_HIGHMEM
> +	 INT_MAX,
>  #endif
> -	 32,
> +	 INT_MAX,
>  };
>
>  EXPORT_SYMBOL(totalram_pages);
> -- 
> 1.9.1

We can also do things like below to make it readable ?

#ifdef CONFIG_ZONE_DMA
	[ZONE_DMA] = 256,
#endif

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>