答复: [PATCH v3] mm/compaction:let proactive compaction order configurable

["Chu,Kaiping" <chukaiping@baidu.com>]

Please see my answer inline.

-----邮件原件-----
发件人: Rafael Aquini <aquini@redhat.com> 
发送时间: 2021年4月26日 9:31
收件人: Chu,Kaiping <chukaiping@baidu.com>
抄送: 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; linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org; linux-mm@kvack.org
主题: Re: [PATCH v3] mm/compaction:let proactive compaction order configurable

On Sun, Apr 25, 2021 at 09:21:02AM +0800, 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>

Two minor nits on the commit log message: 
* there seems to be a whitespage missing in your short log: 
  "... mm/compaction:let ..."
--> I will fix it in next patch.

* has the path really been reported by a test robot?
--> Yes. There is a compile error in v1, I fixed it in v2.

A note on the sysctl name, I'd suggest that it perhaps should reflect the fact that we're adjusting the order for proactive compation.
How about "proactive_compation_order"?
--> I will change it in next patch.

Cheers,

> ---
> 
> 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            |    9 ++++++---
>  3 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h 
> index ed4070e..151ccd1 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_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..e50f7d2 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       = "compaction_order",
> +		.data           = &sysctl_compaction_order,
> +		.maxlen         = sizeof(sysctl_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..70c0acd 
> 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1925,16 +1925,16 @@ 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_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_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
> + * wrt to the sysctl_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 @@ -2666,6 +2666,7 @@ 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_compaction_order;
>  
>  /*
>   * This is the entry point for compacting all nodes via @@ -2958,6 
> +2959,8 @@ static int __init kcompactd_init(void)
>  	int nid;
>  	int ret;
>  
> +	sysctl_compaction_order = COMPACTION_HPAGE_ORDER;
> +
>  	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
>  					"mm/compaction:online",
>  					kcompactd_cpu_online, NULL);
> --
> 1.7.1
>