linux-kernel - Re: [PATCH v3 6/6] mm: khugepaged: set to next mm direct when mm has MMF_DISABLE_THP

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Message-ID: <20260105003128.7xitfioeno56h7f3@master>
Date: Mon, 5 Jan 2026 00:31:28 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Lance Yang <lance.yang@...ux.dev>
Cc: Vernon Yang <vernon2gm@...il.com>, lorenzo.stoakes@...cle.com,
	ziy@...dia.com, dev.jain@....com, baohua@...nel.org,
	richard.weiyang@...il.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, david@...nel.org,
	Vernon Yang <yanglincheng@...inos.cn>, akpm@...ux-foundation.org
Subject: Re: [PATCH v3 6/6] mm: khugepaged: set to next mm direct when mm has
 MMF_DISABLE_THP_COMPLETELY

On Sun, Jan 04, 2026 at 08:20:29PM +0800, Lance Yang wrote:
>
>
>On 2026/1/4 13:41, Vernon Yang wrote:
>> When an mm with the MMF_DISABLE_THP_COMPLETELY flag is detected during
>> scanning, directly set khugepaged_scan.mm_slot to the next mm_slot,
>> reduce redundant operation.
>> 
>> Signed-off-by: Vernon Yang <yanglincheng@...inos.cn>
>> ---
>>   mm/khugepaged.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index 1ca034a5f653..d4ed0f397335 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -2541,7 +2541,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
>>   	 * Release the current mm_slot if this mm is about to die, or
>>   	 * if we scanned all vmas of this mm.
>>   	 */
>> -	if (hpage_collapse_test_exit(mm) || !vma) {
>> +	if (hpage_collapse_test_exit_or_disable(mm) || !vma) {
>>   		/*
>>   		 * Make sure that if mm_users is reaching zero while
>>   		 * khugepaged runs here, khugepaged_exit will find
>
>
>Let's convert hpage_collapse_test_exit() in collect_mm_slot() as well,
>otherwise the mm_slot would not be freed and will be scanned again ...
>
>static void collect_mm_slot(struct mm_slot *slot)
>{
>	struct mm_struct *mm = slot->mm;
>
>	lockdep_assert_held(&khugepaged_mm_lock);
>
>	if (hpage_collapse_test_exit(mm)) { <-
>

What if user toggle the MMF_DISABLE_THP_COMPLETELY flag again?

>		hash_del(&slot->hash);
>		list_del(&slot->mm_node);
>
>		mm_slot_free(mm_slot_cache, slot);
>		mmdrop(mm);
>	}
>}

-- 
Wei Yang
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