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Date:   Tue, 29 Mar 2022 01:52:30 +0000
From:   Wei Yang <richard.weiyang@gmail.com>
To:     "Huang, Ying" <ying.huang@intel.com>
Cc:     Wei Yang <richard.weiyang@gmail.com>, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        mgorman@techsingularity.net
Subject: Re: [PATCH 2/2] mm/vmscan: make sure wakeup_kswapd with managed zone
Message-ID: <20220329015230.hneciyfxoxtvfytl@master>
Reply-To: Wei Yang <richard.weiyang@gmail.com>
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 <875ynxh9lg.fsf@yhuang6-desk2.ccr.corp.intel.com>
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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))) {
 		if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING))
 			return 0;
-		for (z = pgdat->nr_zones - 1; z >= 0; z--) {
-			if (managed_zone(pgdat->node_zones + z))
-				break;
-		}
-		wakeup_kswapd(pgdat->node_zones + z, 0, order, ZONE_MOVABLE);
+
+		wakeup_kswapd(zone, 0, order, ZONE_MOVABLE);
 		return 0;
 	}
 
-- 
2.33.1


>Best Regards,
>Huang, Ying

-- 
Wei Yang
Help you, Help me