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

Wei Yang
2022-03-30T00:14:31Z

On Tue, Mar 29, 2022 at 10:05:20AM +0800, Huang, Ying wrote:
>Wei Yang <richard.weiyang@gmail.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@gmail.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@gmail.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