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

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Date:   Mon, 28 Mar 2022 15:23:49 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     "Huang, Ying" <ying.huang@...el.com>,
        Wei Yang <richard.weiyang@...il.com>
CC:     <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 2022/3/28 9:08, Huang, Ying wrote:
> Hi, Wei,
> 
> Wei Yang <richard.weiyang@...il.com> writes:
> 
>> wakeup_kswapd() only wake up kswapd when the zone is managed.
>>
>> For two callers of wakeup_kswapd(), they are node perspective.
>>
>>   * wake_all_kswapds
>>   * numamigrate_isolate_page
>>
>> If we picked up a !managed zone, this is not we expected.
>>
>> This patch makes sure we pick up a managed zone for wakeup_kswapd().
>>
>> Signed-off-by: Wei Yang <richard.weiyang@...il.com>
>> ---
>>  mm/migrate.c    | 2 +-
>>  mm/page_alloc.c | 2 ++
>>  2 files changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 3d60823afd2d..c4b654c0bdf0 100644
>> --- 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?

This patch looks good to me too. Thanks!

BTW: This makes me remember the bewilderment when I read the relevant code.
It's very kind of you if you could tell me the difference between
managed_zone and populated_zone. IIUC, when the caller relies on the
activity from buddy system, managed_zone should always be used. I think
there're many places like compaction need to use managed_zone but
populated_zone is used now. They might need to change to use managed_zone
too. Or am I miss something?

Many Thanks. :)

> 
>>  				break;
>>  		}
>>  		wakeup_kswapd(pgdat->node_zones + z, 0, order, ZONE_MOVABLE);
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 4c0c4ef94ba0..6656c2d06e01 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -4674,6 +4674,8 @@ static void wake_all_kswapds(unsigned int order, gfp_t gfp_mask,
>>  
>>  	for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, highest_zoneidx,
>>  					ac->nodemask) {
>> +		if (!managed_zone(zone))
>> +			continue;
>>  		if (last_pgdat != zone->zone_pgdat)
>>  			wakeup_kswapd(zone, gfp_mask, order, highest_zoneidx);
>>  		last_pgdat = zone->zone_pgdat;
> 
> Best Regards,
> Huang, Ying
> 
> .
>