linux-kernel - Re: [PATCH v2 2/4] mm/hugetlb: fix two comments related to huge_pmd

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Message-ID: <b4898184-ee7b-4e37-860e-5790339059a3@kernel.org>
Date: Sun, 21 Dec 2025 10:26:42 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Nadav Amit <nadav.amit@...il.com>
Cc: Harry Yoo <harry.yoo@...cle.com>,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 linux-arch@...r.kernel.org, "open list:MEMORY MANAGEMENT"
 <linux-mm@...ck.org>, Will Deacon <will@...nel.org>,
 "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>, Nick Piggin <npiggin@...il.com>,
 Peter Zijlstra <peterz@...radead.org>, Arnd Bergmann <arnd@...db.de>,
 Muchun Song <muchun.song@...ux.dev>, Oscar Salvador <osalvador@...e.de>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
 Pedro Falcato <pfalcato@...e.de>, Rik van Riel <riel@...riel.com>,
 Laurence Oberman <loberman@...hat.com>,
 Prakash Sangappa <prakash.sangappa@...cle.com>,
 Liu Shixin <liushixin2@...wei.com>
Subject: Re: [PATCH v2 2/4] mm/hugetlb: fix two comments related to
 huge_pmd_unshare()

>>>>
>>>> Whoever is the last owner of a (previously) shared page table must unmap any
>>>> contained pages (adjust mapcount/ref, sync a/d bit, ...).
>>> Right.
>>>> So it's not just a matter of deferring the freeing, because these page tables
>>>> will still contain content.
>>> I was (and maybe still) bit confused while reading the old comment as
>>> it implied (or maybe I just misread) that by deferring freeing of page tables
>>> we don't have to flush TLB in __unmap_hugepage_range() and can flush later
>>> instead.
>>
>> Yeah, I am also confused by the old comment. I think the idea there was to drop the reference only later and thereby deferred-free the page.
> 
> My bad. I looked again, and the comment indeed doesn’t make much sense. Thanks for fixing it.

No worries, thanks for taking a look!

-- 
Cheers

David