linux-kernel - Re: [PATCH v1 2/4] mm/hugetlb: fix two comments related to huge_pmd

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Message-ID: <aTpZdhXljlYcnek7@localhost.localdomain>
Date: Thu, 11 Dec 2025 06:41:10 +0100
From: Oscar Salvador <osalvador@...e.de>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	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>,
	"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>,
	Harry Yoo <harry.yoo@...cle.com>,
	Laurence Oberman <loberman@...hat.com>,
	Prakash Sangappa <prakash.sangappa@...cle.com>,
	Nadav Amit <nadav.amit@...il.com>,
	Liu Shixin <liushixin2@...wei.com>
Subject: Re: [PATCH v1 2/4] mm/hugetlb: fix two comments related to
 huge_pmd_unshare()

On Fri, Dec 05, 2025 at 10:35:56PM +0100, David Hildenbrand (Red Hat) wrote:
> Ever since we stopped using the page count to detect shared PMD
> page tables, these comments are outdated.
> 
> The only reason we have to flush the TLB early is because once we drop
> the i_mmap_rwsem, the previously shared page table could get freed (to
> then get reallocated and used for other purpose). So we really have to
> flush the TLB before that could happen.
> 
> So let's simplify the comments a bit.
> 
> The "If we unshared PMDs, the TLB flush was not recorded in mmu_gather."
> part introduced as in commit a4a118f2eead ("hugetlbfs: flush TLBs
> correctly after huge_pmd_unshare") was confusing: sure it is recorded
> in the mmu_gather, otherwise tlb_flush_mmu_tlbonly() wouldn't do
> anything. So let's drop that comment while at it as well.
> 
> We'll centralize these comments in a single helper as we rework the code
> next.
> 
> Fixes: 59d9094df3d7 ("mm: hugetlb: independent PMD page table shared count")
> Cc: Liu Shixin <liushixin2@...wei.com>
> Signed-off-by: David Hildenbrand (Red Hat) <david@...nel.org>

Acked-by: Oscar Salvador <osalvador@...e.de>


-- 
Oscar Salvador
SUSE Labs