linux-kernel - Re: [PATCH 2/2] mm/vmscan: make sure wakeup

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Message-ID: <20220330001427.a745zl3qej2fajmf@master>
Date:   Wed, 30 Mar 2022 00:14:27 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Wei Yang <richard.weiyang@...il.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        mgorman@...hsingularity.net
Subject: Re: [PATCH 2/2] mm/vmscan: make sure wakeup_kswapd with managed zone

On Tue, Mar 29, 2022 at 10:05:20AM +0800, Huang, Ying wrote:
>Wei Yang <richard.weiyang@...il.com> writes:
>
>> On Tue, Mar 29, 2022 at 08:43:23AM +0800, Huang, Ying wrote:
>> [...]
>>>>>> --- a/mm/migrate.c
>>>>>> +++ b/mm/migrate.c
>>>>>> @@ -2046,7 +2046,7 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
>>>>>>  		if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING))
>>>>>>  			return 0;
>>>>>>  		for (z = pgdat->nr_zones - 1; z >= 0; z--) {
>>>>>> -			if (populated_zone(pgdat->node_zones + z))
>>>>>> +			if (managed_zone(pgdat->node_zones + z))
>>>>>
>>>>>This looks good to me!  Thanks!  It seems that we can replace
>>>>>populated_zone() in migrate_balanced_pgdat() too.  Right?
>>>>>
>>>>
>>>> Yes, you are right. I didn't spot this.
>>>>
>>>> While this patch comes from the clue of wakeup_kswapd(), I am not sure it is
>>>> nice to put it in this patch together.
>>>>
>>>> Which way you prefer to include this: merge the change into this one, or a
>>>> separate one?
>>>
>>>Either is OK for me.
>>>
>>
>> After reading the code, I am willing to do a little simplification. Does this
>> look good to you?
>>
>> From 85c8a5cd708ada3e9f5b0409413407b7be1bc446 Mon Sep 17 00:00:00 2001
>> From: Wei Yang <richard.weiyang@...il.com>
>> Date: Tue, 29 Mar 2022 09:24:36 +0800
>> Subject: [PATCH] mm/migrate.c: return valid zone for wakeup_kswapd from
>>  migrate_balanced_pgdat()
>>
>> To wakeup kswapd, we need to iterate pgdat->node_zones and get the
>> proper zone. While this work has already been done in
>> migrate_balanced_pgdat().
>>
>> Let's return the valid zone directly instead of do the iteration again.
>>
>> Signed-off-by: Wei Yang <richard.weiyang@...il.com>
>> ---
>>  mm/migrate.c | 21 ++++++++-------------
>>  1 file changed, 8 insertions(+), 13 deletions(-)
>>
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 5adc55b5347c..b086bd781956 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -1973,7 +1973,7 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
>>   * Returns true if this is a safe migration target node for misplaced NUMA
>>   * pages. Currently it only checks the watermarks which is crude.
>>   */
>> -static bool migrate_balanced_pgdat(struct pglist_data *pgdat,
>> +static struct zone *migrate_balanced_pgdat(struct pglist_data *pgdat,
>>  				   unsigned long nr_migrate_pages)
>>  {
>>  	int z;
>> @@ -1985,14 +1985,13 @@ static bool migrate_balanced_pgdat(struct pglist_data *pgdat,
>>  			continue;
>>  
>>  		/* Avoid waking kswapd by allocating pages_to_migrate pages. */
>> -		if (!zone_watermark_ok(zone, 0,
>> +		if (zone_watermark_ok(zone, 0,
>>  				       high_wmark_pages(zone) +
>>  				       nr_migrate_pages,
>>  				       ZONE_MOVABLE, 0))
>> -			continue;
>> -		return true;
>> +			return zone;
>>  	}
>> -	return false;
>> +	return NULL;
>>  }
>>  
>>  static struct page *alloc_misplaced_dst_page(struct page *page,
>> @@ -2032,6 +2031,7 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
>>  	int page_lru;
>>  	int nr_pages = thp_nr_pages(page);
>>  	int order = compound_order(page);
>> +	struct zone *zone;
>>  
>>  	VM_BUG_ON_PAGE(order && !PageTransHuge(page), page);
>>  
>> @@ -2040,16 +2040,11 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
>>  		return 0;
>>  
>>  	/* Avoid migrating to a node that is nearly full */
>> -	if (!migrate_balanced_pgdat(pgdat, nr_pages)) {
>> -		int z;
>> -
>> +	if ((zone = migrate_balanced_pgdat(pgdat, nr_pages))) {
>
>I think that this reverses the original semantics.  Originally, we give
>up and wake up kswapd if there's no enough free pages on the target
>node.  But now, you give up and wake up if there's enough free pages.
>

You are right, I misunderstand it.

Sorry


-- 
Wei Yang
Help you, Help me