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From: Lance Yang Date: Mon, 6 Oct 2025 14:48:35 +0800 X-Gmail-Original-Message-ID: X-Gm-Features: AS18NWC1StCtK5OBsLdKS2Uo36btm8pgGL6VfozmsZHbDnUVCBhw4W8BmS1RLoQ Message-ID: Subject: Re: [PATCH] mm/dirty: Replace READ_ONCE() with pudp_get() To: Anshuman Khandual Cc: Dev Jain , linux-mm@kvack.org, Andrew Morton , David Hildenbrand , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: C8EBF4000C X-Stat-Signature: oxwzm513d4audo4cer1jqhrtxt39muyc X-HE-Tag: 1759733356-75702 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Oct 6, 2025 at 2:28=E2=80=AFPM Anshuman Khandual wrote: > > > > On 06/10/25 11:37 AM, Dev Jain wrote: > > > > On 06/10/25 11:22 am, Anshuman Khandual wrote: > >> Replace READ_ONCE() with a standard page table accessor i.e pudp_get()= that > >> anyways defaults into READ_ONCE() in cases where platform does not ove= rride Nice cleanup! > >> > >> Cc: Andrew Morton > >> Cc: David Hildenbrand > >> Cc: linux-mm@kvack.org > >> Cc: linux-kernel@vger.kernel.org > >> Signed-off-by: Anshuman Khandual > >> --- > >> mm/mapping_dirty_helpers.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/mm/mapping_dirty_helpers.c b/mm/mapping_dirty_helpers.c > >> index c193de6cb23a..737c407f4081 100644 > >> --- a/mm/mapping_dirty_helpers.c > >> +++ b/mm/mapping_dirty_helpers.c > >> @@ -149,7 +149,7 @@ static int wp_clean_pud_entry(pud_t *pud, unsigned= long addr, unsigned long end, > >> struct mm_walk *walk) > >> { > >> #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD > >> - pud_t pudval =3D READ_ONCE(*pud); > >> + pud_t pudval =3D pudp_get(pud); > >> /* Do not split a huge pud */ > >> if (pud_trans_huge(pudval)) { > > > > Talking about mm, why not also make changes for these READ_ONCE accesse= s > > in gup, hmm, memory, mprotect, sparse-vmemmap? Yep, I agree with Dev on that one. Because the change is assumed to be a no-op on all architectures for now, right? > > > > Right, could replace all mm/ READ_ONCE() for pxdp pointers with the pgtab= le helpers > but that will create too much code churn in a single patch. Thought of do= ing these > replacements per file will be much more contained which is easy both for = review and > testing. Emm... as pointed out by Dev, it would get the entire cleanup done in one go, avoiding the churn of multiple small patches ;) Cheers, Lance