linux-kernel - Re: [RFC PATCH] mm: Enable khugepaged to operate on non-writable VMAs

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Message-ID: <9c3a2ecd-ceae-4e87-a6d7-6a7121ab7a15@redhat.com>
Date: Mon, 1 Sep 2025 10:32:34 +0200
From: David Hildenbrand <david@...hat.com>
To: Kiryl Shutsemau <kas@...nel.org>, Dev Jain <dev.jain@....com>
Cc: akpm@...ux-foundation.org, willy@...radead.org, hughd@...gle.com,
 ziy@...dia.com, baolin.wang@...ux.alibaba.com, lorenzo.stoakes@...cle.com,
 Liam.Howlett@...cle.com, npache@...hat.com, ryan.roberts@....com,
 baohua@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm: Enable khugepaged to operate on non-writable VMAs


>> @@ -676,9 +676,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
>>   			writable = true;
>>   	}
>>   
>> -	if (unlikely(!writable)) {
>> -		result = SCAN_PAGE_RO;
>> -	} else if (unlikely(cc->is_khugepaged && !referenced)) {
>> +	if (unlikely(cc->is_khugepaged && !referenced)) {
>>   		result = SCAN_LACK_REFERENCED_PAGE;
>>   	} else {
>>   		result = SCAN_SUCCEED;
>> @@ -1421,9 +1419,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
>>   		     mmu_notifier_test_young(vma->vm_mm, _address)))
>>   			referenced++;
>>   	}
>> -	if (!writable) {
>> -		result = SCAN_PAGE_RO;
>> -	} else if (cc->is_khugepaged &&
>> +	if (cc->is_khugepaged &&
> 
> The only practical use of the writable is gone. The only other usage is
> tracing which can be dropped to as it is not actionable anymore.
> 
> Could you drop writable? Maybe as a separate commit.

I think we should just do it in the same patch.

-- 
Cheers

David / dhildenb