linux-kernel - Re: [PATCH HOTFIX 6.17] mm/mremap: avoid expensive folio lookup on mremap folio pte batch

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Message-ID: <dbd8c326-8848-486f-8789-3528dea2bb28@redhat.com>
Date: Mon, 11 Aug 2025 17:19:26 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Barry Song <21cnbao@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
 Pedro Falcato <pfalcato@...e.de>, Dev Jain <dev.jain@....com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH HOTFIX 6.17] mm/mremap: avoid expensive folio lookup on
 mremap folio pte batch

>>
>> Unless the previous contpte_try_unfold() was very costly and removing it yielded
>> a significant improvement, it’s difficult to see how the benefits would outweigh
>> the drawbacks of vm_normal_folio(). Does this imply that there was already a
>> regression in mremap() caused by contpte_try_unfold() before?
>> And that Dev’s patch is essentially a fix for this regression on arm64?

Fix/regression might be the wrong words here IMHO, but yes, this code 
was not playing nicely with automatic cont-pte folding/unfolding , and 
now it's optimized for that.

-- 
Cheers,

David / dhildenb