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Subject: Re: [PATCH v4] mm/compaction: let proactive compaction order
 configurable
To:     chukaiping <chukaiping@baidu.com>, mcgrof@kernel.org,
        keescook@chromium.org, yzaikin@google.com,
        akpm@linux-foundation.org, vbabka@suse.cz, nigupta@nvidia.com,
        bhe@redhat.com, khalid.aziz@oracle.com, iamjoonsoo.kim@lge.com,
        mateusznosek0@gmail.com, sh_def@163.com
Cc:     linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org
References: <1619576901-9531-1-git-send-email-chukaiping@baidu.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <a3f6628a-8165-429f-0383-c522b4c49197@redhat.com>
Date:   Wed, 9 Jun 2021 12:44:55 +0200
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On 28.04.21 04:28, chukaiping wrote:
> Currently the proactive compaction order is fixed to
> COMPACTION_HPAGE_ORDER(9), it's OK in most machines with lots of
> normal 4KB memory, but it's too high for the machines with small
> normal memory, for example the machines with most memory configured
> as 1GB hugetlbfs huge pages. In these machines the max order of
> free pages is often below 9, and it's always below 9 even with hard
> compaction. This will lead to proactive compaction be triggered very
> frequently. In these machines we only care about order of 3 or 4.
> This patch export the oder to proc and let it configurable
> by user, and the default value is still COMPACTION_HPAGE_ORDER.
> 
> Signed-off-by: chukaiping <chukaiping@baidu.com>
> Reported-by: kernel test robot <lkp@intel.com>
> ---
> 
> Changes in v4:
>      - change the sysctl file name to proactive_compation_order
> 
> Changes in v3:
>      - change the min value of compaction_order to 1 because the fragmentation
>        index of order 0 is always 0
>      - move the definition of max_buddy_zone into #ifdef CONFIG_COMPACTION
> 
> Changes in v2:
>      - fix the compile error in ia64 and powerpc, move the initialization
>        of sysctl_compaction_order to kcompactd_init because
>        COMPACTION_HPAGE_ORDER is a variable in these architectures
>      - change the hard coded max order number from 10 to MAX_ORDER - 1
> 
>   include/linux/compaction.h |    1 +
>   kernel/sysctl.c            |   10 ++++++++++
>   mm/compaction.c            |   12 ++++++++----
>   3 files changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index ed4070e..a0226b1 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -83,6 +83,7 @@ static inline unsigned long compact_gap(unsigned int order)
>   #ifdef CONFIG_COMPACTION
>   extern int sysctl_compact_memory;
>   extern unsigned int sysctl_compaction_proactiveness;
> +extern unsigned int sysctl_proactive_compaction_order;
>   extern int sysctl_compaction_handler(struct ctl_table *table, int write,
>   			void *buffer, size_t *length, loff_t *ppos);
>   extern int sysctl_extfrag_threshold;
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 62fbd09..ed9012e 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -196,6 +196,7 @@ enum sysctl_writes_mode {
>   #endif /* CONFIG_SCHED_DEBUG */
>   
>   #ifdef CONFIG_COMPACTION
> +static int max_buddy_zone = MAX_ORDER - 1;
>   static int min_extfrag_threshold;
>   static int max_extfrag_threshold = 1000;
>   #endif
> @@ -2871,6 +2872,15 @@ int proc_do_static_key(struct ctl_table *table, int write,
>   		.extra2		= &one_hundred,
>   	},
>   	{
> +		.procname       = "proactive_compation_order",
> +		.data           = &sysctl_proactive_compaction_order,
> +		.maxlen         = sizeof(sysctl_proactive_compaction_order),
> +		.mode           = 0644,
> +		.proc_handler   = proc_dointvec_minmax,
> +		.extra1         = SYSCTL_ONE,
> +		.extra2         = &max_buddy_zone,
> +	},
> +	{
>   		.procname	= "extfrag_threshold",
>   		.data		= &sysctl_extfrag_threshold,
>   		.maxlen		= sizeof(int),
> diff --git a/mm/compaction.c b/mm/compaction.c
> index e04f447..171436e 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1925,17 +1925,18 @@ static bool kswapd_is_running(pg_data_t *pgdat)
>   
>   /*
>    * A zone's fragmentation score is the external fragmentation wrt to the
> - * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
> + * sysctl_proactive_compaction_order. It returns a value in the range
> + * [0, 100].
>    */
>   static unsigned int fragmentation_score_zone(struct zone *zone)
>   {
> -	return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
> +	return extfrag_for_order(zone, sysctl_proactive_compaction_order);
>   }
>   
>   /*
>    * A weighted zone's fragmentation score is the external fragmentation
> - * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
> - * returns a value in the range [0, 100].
> + * wrt to the sysctl_proactive_compaction_order scaled by the zone's size.
> + * It returns a value in the range [0, 100].
>    *
>    * The scaling factor ensures that proactive compaction focuses on larger
>    * zones like ZONE_NORMAL, rather than smaller, specialized zones like
> @@ -2666,6 +2667,7 @@ static void compact_nodes(void)
>    * background. It takes values in the range [0, 100].
>    */
>   unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
> +unsigned int __read_mostly sysctl_proactive_compaction_order;
>   
>   /*
>    * This is the entry point for compacting all nodes via
> @@ -2958,6 +2960,8 @@ static int __init kcompactd_init(void)
>   	int nid;
>   	int ret;
>   
> +	sysctl_proactive_compaction_order = COMPACTION_HPAGE_ORDER;
> +
>   	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
>   					"mm/compaction:online",
>   					kcompactd_cpu_online, NULL);
> 

Hm, do we actually want to put an upper limit to the order a user can 
supply?

-- 
Thanks,

David / dhildenb