linux-kernel - Re: [PATCH v1 1/2] mm: drop vm_total

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Message-ID: <CAM9Jb+imokWSRDOHrtJAuCvvbKyjk28LVde2QMFc1YdBsZ=kLA@mail.gmail.com>
Date:   Sun, 21 Jun 2020 21:56:38 +0200
From:   Pankaj Gupta <pankaj.gupta.linux@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Huang Ying <ying.huang@...el.com>,
        Minchan Kim <minchan@...nel.org>,
        Wei Yang <richard.weiyang@...il.com>
Subject: Re: [PATCH v1 1/2] mm: drop vm_total_pages

> The global variable "vm_total_pages" is a relict from older days. There
> is only a single user that reads the variable - build_all_zonelists() -
> and the first thing it does is updating it. Use a local variable in
> build_all_zonelists() instead and drop the local variable.
>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Wei Yang <richard.weiyang@...il.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  include/linux/swap.h | 1 -
>  mm/memory_hotplug.c  | 3 ---
>  mm/page-writeback.c  | 6 ++----
>  mm/page_alloc.c      | 2 ++
>  mm/vmscan.c          | 5 -----
>  5 files changed, 4 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 4c5974bb9ba94..124261acd5d0a 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -371,7 +371,6 @@ extern unsigned long mem_cgroup_shrink_node(struct mem_cgroup *mem,
>  extern unsigned long shrink_all_memory(unsigned long nr_pages);
>  extern int vm_swappiness;
>  extern int remove_mapping(struct address_space *mapping, struct page *page);
> -extern unsigned long vm_total_pages;
>
>  extern unsigned long reclaim_pages(struct list_head *page_list);
>  #ifdef CONFIG_NUMA
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 9b34e03e730a4..d682781cce48d 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -835,8 +835,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>         kswapd_run(nid);
>         kcompactd_run(nid);
>
> -       vm_total_pages = nr_free_pagecache_pages();
> -
>         writeback_set_ratelimit();
>
>         memory_notify(MEM_ONLINE, &arg);
> @@ -1586,7 +1584,6 @@ static int __ref __offline_pages(unsigned long start_pfn,
>                 kcompactd_stop(node);
>         }
>
> -       vm_total_pages = nr_free_pagecache_pages();
>         writeback_set_ratelimit();
>
>         memory_notify(MEM_OFFLINE, &arg);
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 28b3e7a675657..4e4ddd67b71e5 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2076,13 +2076,11 @@ static int page_writeback_cpu_online(unsigned int cpu)
>   * Called early on to tune the page writeback dirty limits.
>   *
>   * We used to scale dirty pages according to how total memory
> - * related to pages that could be allocated for buffers (by
> - * comparing nr_free_buffer_pages() to vm_total_pages.
> + * related to pages that could be allocated for buffers.
>   *
>   * However, that was when we used "dirty_ratio" to scale with
>   * all memory, and we don't do that any more. "dirty_ratio"
> - * is now applied to total non-HIGHPAGE memory (by subtracting
> - * totalhigh_pages from vm_total_pages), and as such we can't
> + * is now applied to total non-HIGHPAGE memory, and as such we can't
>   * get into the old insane situation any more where we had
>   * large amounts of dirty pages compared to a small amount of
>   * non-HIGHMEM memory.
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 0c435b2ed665c..7b0dde69748c1 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5903,6 +5903,8 @@ build_all_zonelists_init(void)
>   */
>  void __ref build_all_zonelists(pg_data_t *pgdat)
>  {
> +       unsigned long vm_total_pages;
> +
>         if (system_state == SYSTEM_BOOTING) {
>                 build_all_zonelists_init();
>         } else {
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index b6d84326bdf2d..0010859747df2 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -170,11 +170,6 @@ struct scan_control {
>   * From 0 .. 200.  Higher means more swappy.
>   */
>  int vm_swappiness = 60;
> -/*
> - * The total number of pages which are beyond the high watermark within all
> - * zones.
> - */
> -unsigned long vm_total_pages;
>
>  static void set_task_reclaim_state(struct task_struct *task,
>                                    struct reclaim_state *rs)

Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@...il.com>