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SubjectRe: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request
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+CC linux-api

On 09/06/2017 06:35 AM, js1304@gmail.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@lge.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 by setting 0 to
> sysctl_lowmem_reserve_ratio[ZONE_HIGHMEM].
>
> 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.
>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> ---
> Documentation/sysctl/vm.txt | 5 ++---
> include/linux/mmzone.h | 2 +-
> mm/page_alloc.c | 25 ++++++++++++++-----------
> 3 files changed, 17 insertions(+), 15 deletions(-)
>
> diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
> index 9baf66a..e9059d3 100644
> --- a/Documentation/sysctl/vm.txt
> +++ b/Documentation/sysctl/vm.txt
> @@ -336,8 +336,6 @@ The lowmem_reserve_ratio is an array. You can see them by reading this file.
> % cat /proc/sys/vm/lowmem_reserve_ratio
> 256 256 32
> -
> -Note: # of this elements is one fewer than number of zones. Because the highest
> - zone's value is not necessary for following calculation.
>
> But, these values are not used directly. The kernel calculates # of protection
> pages for each zones from them. These are shown as array of protection pages
> @@ -388,7 +386,8 @@ As above expression, they are reciprocal number of ratio.
> pages of higher zones on the node.
>
> If you would like to protect more pages, smaller values are effective.
> -The minimum value is 1 (1/1 -> 100%).
> +The minimum value is 1 (1/1 -> 100%). The value less than 1 completely
> +disables protection of the pages.
>
> ==============================================================
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 356a814..d549c4e 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -890,7 +890,7 @@ 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 0f34356..2a7f7e9 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -203,17 +203,18 @@ 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,
> + [ZONE_DMA] = 256,
> #endif
> #ifdef CONFIG_ZONE_DMA32
> - 256,
> + [ZONE_DMA32] = 256,
> #endif
> + [ZONE_NORMAL] = 32,
> #ifdef CONFIG_HIGHMEM
> - 32,
> + [ZONE_HIGHMEM] = 0,
> #endif
> - 32,
> + [ZONE_MOVABLE] = 0,
> };
>
> EXPORT_SYMBOL(totalram_pages);
> @@ -6921,13 +6922,15 @@ static void setup_per_zone_lowmem_reserve(void)
> struct zone *lower_zone;
>
> idx--;
> -
> - if (sysctl_lowmem_reserve_ratio[idx] < 1)
> - sysctl_lowmem_reserve_ratio[idx] = 1;
> -
> lower_zone = pgdat->node_zones + idx;
> - lower_zone->lowmem_reserve[j] = managed_pages /
> - sysctl_lowmem_reserve_ratio[idx];
> +
> + if (sysctl_lowmem_reserve_ratio[idx] < 1) {
> + sysctl_lowmem_reserve_ratio[idx] = 0;
> + lower_zone->lowmem_reserve[j] = 0;
> + } else {
> + lower_zone->lowmem_reserve[j] =
> + managed_pages / sysctl_lowmem_reserve_ratio[idx];
> + }
> managed_pages += lower_zone->managed_pages;
> }
> }
>

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