Re: [PATCH 2/2] mm/vmscan: make sure wakeup_kswapd with managed zone

[Wei Yang <richard.weiyang@gmail.com>]

On Mon, Mar 28, 2022 at 03:23:49PM +0800, Miaohe Lin wrote:
>On 2022/3/28 9:08, Huang, Ying wrote:
>> Hi, Wei,
>> 
>> Wei Yang <richard.weiyang@gmail.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@gmail.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

The difference is managed_zone means the zone has pages managed by buddy,
while populated_zone means the zone has pages but may be reserved.

>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?

This thread comes from the read of commit 6aa303defb74, which adjust the
vmscan code. It looks like there is some mis-use in compaction, but I didn't
get time to go through it.

>
>Many Thanks. :)

-- 
Wei Yang
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