Re: [PATCH v3 1/2] mm: compaction: support triggering of proactive compaction by user

[Charan Teja Kalla <charante@codeaurora.org>]

Just another ping to have your comments.

Thanks in advance!!

On 6/7/2021 4:08 PM, Charan Teja Kalla wrote:
> A gentle ping.
> 
> --Charan
> 
> On 5/31/2021 4:24 PM, Charan Teja Reddy wrote:
>> The proactive compaction[1] gets triggered for every 500msec and run
>> compaction on the node for COMPACTION_HPAGE_ORDER (usually order-9)
>> pages based on the value set to sysctl.compaction_proactiveness.
>> Triggering the compaction for every 500msec in search of
>> COMPACTION_HPAGE_ORDER pages is not needed for all applications,
>> especially on the embedded system usecases which may have few MB's of
>> RAM. Enabling the proactive compaction in its state will endup in
>> running almost always on such systems.
>>
>> Other side, proactive compaction can still be very much useful for
>> getting a set of higher order pages in some controllable
>> manner(controlled by using the sysctl.compaction_proactiveness). Thus on
>> systems where enabling the proactive compaction always may proove not
>> required, can trigger the same from user space on write to its sysctl
>> interface. As an example, say app launcher decide to launch the memory
>> heavy application which can be launched fast if it gets more higher
>> order pages thus launcher can prepare the system in advance by
>> triggering the proactive compaction from userspace.
>>
>> This triggering of proactive compaction is done on a write to
>> sysctl.compaction_proactiveness by user.
>>
>> [1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=facdaa917c4d5a376d09d25865f5a863f906234a
>>
>> Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
>> ---
>> changes in V2:
>>  - https://lore.kernel.org/patchwork/patch/1431283/
>>
>> changes in V1:
>>  -  https://lore.kernel.org/lkml/1619098678-8501-1-git-send-email-charante@codeaurora.org/
>>
>>  Documentation/admin-guide/sysctl/vm.rst |  3 ++-
>>  include/linux/compaction.h              |  2 ++
>>  include/linux/mmzone.h                  |  1 +
>>  kernel/sysctl.c                         |  2 +-
>>  mm/compaction.c                         | 44 ++++++++++++++++++++++++++++++---
>>  5 files changed, 47 insertions(+), 5 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
>> index 586cd4b..5e8097d 100644
>> --- a/Documentation/admin-guide/sysctl/vm.rst
>> +++ b/Documentation/admin-guide/sysctl/vm.rst
>> @@ -126,7 +126,8 @@ compaction_proactiveness
>>  
>>  This tunable takes a value in the range [0, 100] with a default value of
>>  20. This tunable determines how aggressively compaction is done in the
>> -background. Setting it to 0 disables proactive compaction.
>> +background. On write of non zero value to this tunable will immediately
>> +trigger the proactive compaction. Setting it to 0 disables proactive compaction.
>>  
>>  Note that compaction has a non-trivial system-wide impact as pages
>>  belonging to different processes are moved around, which could also lead
>> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
>> index 4221888..04d5d9f 100644
>> --- a/include/linux/compaction.h
>> +++ b/include/linux/compaction.h
>> @@ -84,6 +84,8 @@ static inline unsigned long compact_gap(unsigned int order)
>>  extern unsigned int sysctl_compaction_proactiveness;
>>  extern int sysctl_compaction_handler(struct ctl_table *table, int write,
>>  			void *buffer, size_t *length, loff_t *ppos);
>> +extern int compaction_proactiveness_sysctl_handler(struct ctl_table *table,
>> +		int write, void *buffer, size_t *length, loff_t *ppos);
>>  extern int sysctl_extfrag_threshold;
>>  extern int sysctl_compact_unevictable_allowed;
>>  
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index 0d53eba..9455809 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -815,6 +815,7 @@ typedef struct pglist_data {
>>  	enum zone_type kcompactd_highest_zoneidx;
>>  	wait_queue_head_t kcompactd_wait;
>>  	struct task_struct *kcompactd;
>> +	bool proactive_compact_trigger;
>>  #endif
>>  	/*
>>  	 * This is a per-node reserve of pages that are not available
>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>> index 14edf84..bed2fad 100644
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -2840,7 +2840,7 @@ static struct ctl_table vm_table[] = {
>>  		.data		= &sysctl_compaction_proactiveness,
>>  		.maxlen		= sizeof(sysctl_compaction_proactiveness),
>>  		.mode		= 0644,
>> -		.proc_handler	= proc_dointvec_minmax,
>> +		.proc_handler	= compaction_proactiveness_sysctl_handler,
>>  		.extra1		= SYSCTL_ZERO,
>>  		.extra2		= &one_hundred,
>>  	},
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 84fde27..197e203 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -2708,6 +2708,30 @@ static void compact_nodes(void)
>>   */
>>  unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
>>  
>> +int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write,
>> +		void *buffer, size_t *length, loff_t *ppos)
>> +{
>> +	int rc, nid;
>> +
>> +	rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
>> +	if (rc)
>> +		return rc;
>> +
>> +	if (write && sysctl_compaction_proactiveness) {
>> +		for_each_online_node(nid) {
>> +			pg_data_t *pgdat = NODE_DATA(nid);
>> +
>> +			if (pgdat->proactive_compact_trigger)
>> +				continue;
>> +
>> +			pgdat->proactive_compact_trigger = true;
>> +			wake_up_interruptible(&pgdat->kcompactd_wait);
>> +		}
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>>  /*
>>   * This is the entry point for compacting all nodes via
>>   * /proc/sys/vm/compact_memory
>> @@ -2752,7 +2776,8 @@ void compaction_unregister_node(struct node *node)
>>  
>>  static inline bool kcompactd_work_requested(pg_data_t *pgdat)
>>  {
>> -	return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
>> +	return pgdat->kcompactd_max_order > 0 || kthread_should_stop() ||
>> +		pgdat->proactive_compact_trigger;
>>  }
>>  
>>  static bool kcompactd_node_suitable(pg_data_t *pgdat)
>> @@ -2905,7 +2930,8 @@ static int kcompactd(void *p)
>>  		trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
>>  		if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
>>  			kcompactd_work_requested(pgdat),
>> -			msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
>> +			msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC)) &&
>> +			!pgdat->proactive_compact_trigger) {
>>  
>>  			psi_memstall_enter(&pflags);
>>  			kcompactd_do_work(pgdat);
>> @@ -2917,10 +2943,20 @@ static int kcompactd(void *p)
>>  		if (should_proactive_compact_node(pgdat)) {
>>  			unsigned int prev_score, score;
>>  
>> -			if (proactive_defer) {
>> +			/*
>> +			 * On wakeup of proactive compaction by sysctl
>> +			 * write, ignore the accumulated defer score.
>> +			 * Anyway, if the proactive compaction didn't
>> +			 * make any progress for the new value, it will
>> +			 * be further deferred by 2^COMPACT_MAX_DEFER_SHIFT
>> +			 * times.
>> +			 */
>> +			if (proactive_defer &&
>> +				!pgdat->proactive_compact_trigger) {
>>  				proactive_defer--;
>>  				continue;
>>  			}
>> +
>>  			prev_score = fragmentation_score_node(pgdat);
>>  			proactive_compact_node(pgdat);
>>  			score = fragmentation_score_node(pgdat);
>> @@ -2931,6 +2967,8 @@ static int kcompactd(void *p)
>>  			proactive_defer = score < prev_score ?
>>  					0 : 1 << COMPACT_MAX_DEFER_SHIFT;
>>  		}
>> +		if (pgdat->proactive_compact_trigger)
>> +			pgdat->proactive_compact_trigger = false;
>>  	}
>>  
>>  	return 0;
>>
> 

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