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Date: Thu, 3 Dec 2015 17:39:35 +0100
From: Michal Hocko <mhocko@...nel.org>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: page_alloc: generalize the dirty balance reserve
On Mon 30-11-15 15:00:21, Johannes Weiner wrote:
> The dirty balance reserve that dirty throttling has to consider is
> merely memory not available to userspace allocations. There is nothing
> writeback-specific about it. Generalize the name so that it's reusable
> outside of that context.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
Acked-by: Michal Hocko <mhocko@...e.com>
> ---
> include/linux/mmzone.h | 6 +++---
> include/linux/swap.h | 1 -
> mm/page-writeback.c | 14 ++++++++++++--
> mm/page_alloc.c | 21 +++------------------
> 4 files changed, 18 insertions(+), 24 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index e23a9e7..9134ae3 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -361,10 +361,10 @@ struct zone {
> struct per_cpu_pageset __percpu *pageset;
>
> /*
> - * This is a per-zone reserve of pages that should not be
> - * considered dirtyable memory.
> + * This is a per-zone reserve of pages that are not available
> + * to userspace allocations.
> */
> - unsigned long dirty_balance_reserve;
> + unsigned long totalreserve_pages;
>
> #ifndef CONFIG_SPARSEMEM
> /*
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 7ba7dcc..066bd21 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -287,7 +287,6 @@ static inline void workingset_node_shadows_dec(struct radix_tree_node *node)
> /* linux/mm/page_alloc.c */
> extern unsigned long totalram_pages;
> extern unsigned long totalreserve_pages;
> -extern unsigned long dirty_balance_reserve;
> extern unsigned long nr_free_buffer_pages(void);
> extern unsigned long nr_free_pagecache_pages(void);
>
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 2c90357..8e5f2fd 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -278,7 +278,12 @@ static unsigned long zone_dirtyable_memory(struct zone *zone)
> unsigned long nr_pages;
>
> nr_pages = zone_page_state(zone, NR_FREE_PAGES);
> - nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
> + /*
> + * Pages reserved for the kernel should not be considered
> + * dirtyable, to prevent a situation where reclaim has to
> + * clean pages in order to balance the zones.
> + */
> + nr_pages -= min(nr_pages, zone->totalreserve_pages);
>
> nr_pages += zone_page_state(zone, NR_INACTIVE_FILE);
> nr_pages += zone_page_state(zone, NR_ACTIVE_FILE);
> @@ -332,7 +337,12 @@ static unsigned long global_dirtyable_memory(void)
> unsigned long x;
>
> x = global_page_state(NR_FREE_PAGES);
> - x -= min(x, dirty_balance_reserve);
> + /*
> + * Pages reserved for the kernel should not be considered
> + * dirtyable, to prevent a situation where reclaim has to
> + * clean pages in order to balance the zones.
> + */
> + x -= min(x, totalreserve_pages);
>
> x += global_page_state(NR_INACTIVE_FILE);
> x += global_page_state(NR_ACTIVE_FILE);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 17a3c66..e786d7e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -114,13 +114,6 @@ static DEFINE_SPINLOCK(managed_page_count_lock);
> unsigned long totalram_pages __read_mostly;
> unsigned long totalreserve_pages __read_mostly;
> unsigned long totalcma_pages __read_mostly;
> -/*
> - * When calculating the number of globally allowed dirty pages, there
> - * is a certain number of per-zone reserves that should not be
> - * considered dirtyable memory. This is the sum of those reserves
> - * over all existing zones that contribute dirtyable memory.
> - */
> -unsigned long dirty_balance_reserve __read_mostly;
>
> int percpu_pagelist_fraction;
> gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
> @@ -5955,20 +5948,12 @@ static void calculate_totalreserve_pages(void)
>
> if (max > zone->managed_pages)
> max = zone->managed_pages;
> +
> + zone->totalreserve_pages = max;
> +
> reserve_pages += max;
> - /*
> - * Lowmem reserves are not available to
> - * GFP_HIGHUSER page cache allocations and
> - * kswapd tries to balance zones to their high
> - * watermark. As a result, neither should be
> - * regarded as dirtyable memory, to prevent a
> - * situation where reclaim has to clean pages
> - * in order to balance the zones.
> - */
> - zone->dirty_balance_reserve = max;
> }
> }
> - dirty_balance_reserve = reserve_pages;
> totalreserve_pages = reserve_pages;
> }
>
> --
> 2.6.2
>
> --
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--
Michal Hocko
SUSE Labs
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