Re: [PATCH V2] mm: compaction: support triggering of proactive compaction by user

Re: [PATCH V2] mm: compaction: support triggering of proactive compaction by user

[Vlastimil Babka]

+CC linux-api

On 5/18/21 3:37 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>

Cancelling all current sleeps immediately when the controlling variable changes
doesn't sound wrong to me.
A question below:

> ---
> changes in V2: 
>     - remove /proc interface trigger for proactive compaction
>     - Intention is same that add a way to trigger proactive compaction by user.
> 
> changes in V1:
>     -  https://lore.kernel.org/lkml/1619098678-8501-1-git-send-email-charante@codeaurora.org/
> 
>  include/linux/compaction.h |  2 ++
>  include/linux/mmzone.h     |  1 +
>  kernel/sysctl.c            |  2 +-
>  mm/compaction.c            | 35 ++++++++++++++++++++++++++++++++---
>  4 files changed, 36 insertions(+), 4 deletions(-)
> 
> 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..9056693 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);
> @@ -2919,7 +2945,7 @@ static int kcompactd(void *p)
>  
>  			if (proactive_defer) {
>  				proactive_defer--;
> -				continue;
> +				goto loop;

I don't understand this part. If we kick kcompactd from the sysctl handler
because we are changing proactiveness, shouldn't we also discard any accumulated
defer score?

>  			}
>  			prev_score = fragmentation_score_node(pgdat);
>  			proactive_compact_node(pgdat);
> @@ -2931,6 +2957,9 @@ static int kcompactd(void *p)
>  			proactive_defer = score < prev_score ?
>  					0 : 1 << COMPACT_MAX_DEFER_SHIFT;
>  		}
> +loop:
> +		if (pgdat->proactive_compact_trigger)
> +			pgdat->proactive_compact_trigger = false;
>  	}
>  
>  	return 0;
> 

Re: [PATCH V2] mm: compaction: support triggering of proactive compaction by user

[Charan Teja Kalla]

Thanks Vlastimil for your inputs!!

On 5/28/2021 8:49 PM, Vlastimil Babka wrote:
> On 5/18/21 3:37 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.
>> 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>
> Cancelling all current sleeps immediately when the controlling variable changes
> doesn't sound wrong to me.

Agree that cancelling sleeps is not wrong here.

> A question below:
> 
>> ---
>> changes in V2: 
>>     - remove /proc interface trigger for proactive compaction
>>     - Intention is same that add a way to trigger proactive compaction by user.
>>  			if (proactive_defer) {
>>  				proactive_defer--;
>> -				continue;
>> +				goto loop;
> I don't understand this part. If we kick kcompactd from the sysctl handler
> because we are changing proactiveness, shouldn't we also discard any accumulated
> defer score?

Yes, we should be discarding the accumulated defer score when user
changing the proactiveness, even when writing higher proactiveness value
than for which it was deferred. Will raise V3 for this.

> 

--Charan
-- 
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