linux-kernel - Re: [PATCH mm-new v3 1/1] mm/khugepaged: abort collapse scan on non-swap entries

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Message-ID: <2e22cff1-fad7-45a6-bdd4-d5921d12c5e2@linux.dev>
Date: Tue, 14 Oct 2025 22:37:28 +0800
From: Lance Yang <lance.yang@...ux.dev>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 David Hildenbrand <david@...hat.com>
Cc: akpm@...ux-foundation.org, Liam.Howlett@...cle.com, baohua@...nel.org,
 baolin.wang@...ux.alibaba.com, dev.jain@....com, hughd@...gle.com,
 ioworker0@...il.com, kirill@...temov.name, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, mpenttil@...hat.com, npache@...hat.com,
 ryan.roberts@....com, ziy@...dia.com, richard.weiyang@...il.com
Subject: Re: [PATCH mm-new v3 1/1] mm/khugepaged: abort collapse scan on
 non-swap entries



On 2025/10/14 22:32, David Hildenbrand wrote:
> 
>> static inline int pte_protnone(pte_t pte)
>> {
>>     return (pte_flags(pte) & (_PAGE_PROTNONE | _PAGE_PRESENT))
>>         == _PAGE_PROTNONE;
>> }
>>
>> static inline int pte_present(pte_t a)
>> {
>>     return pte_flags(a) & (_PAGE_PRESENT | _PAGE_PROTNONE);
>> }
>> ```
>>
>> On x86, pte_present() returns true for a protnone pte. And I'd assume
>> other archs behave similarly ...
> 
> Applies to all architecture. prot-none entries must be present, 
> otherwise we'd have a lot of other issues :)

Thanks for confirming, David! That's good to know ;p

So @Lorenzo, looks like we're good here on the protnone front. Does
that clear up your concern?