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Fri, 7 Nov 2025 07:50:26 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface MIME-Version: 1.0 X-ThreadId: AvUhhSuyoH3V Date: Fri, 07 Nov 2025 13:50:06 +0100 From: "Arnd Bergmann" To: "Lance Yang" , "Huacai Chen" Cc: "Andrew Morton" , "Huacai Chen" , "Jan Kara" , "Kevin Brodsky" , Linux-Arch , linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org, "Lorenzo Stoakes" , vishal.moola@gmail.com, "Lance Yang" Message-Id: In-Reply-To: <20251107114455.59111-1-ioworker0@gmail.com> References: <20251107095922.3106390-1-chenhuacai@loongson.cn> <20251107114455.59111-1-ioworker0@gmail.com> Subject: Re: [PATCH Resend] mm: Refine __{pgd,p4d,pud,pmd,pte}_alloc_one_*() about HIGHMEM Content-Type: text/plain Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 384FA20005 X-Stat-Signature: 5bzgy6cz5j4xznrptmtjfxtrii5m3cdt X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1762519828-342459 X-HE-Meta: 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 clr/2fYE Ob7qQpzoty0bSw1Vw6kijLqY5W5PEOAjR9EvoyE/j5H1nq74= 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 Fri, Nov 7, 2025, at 12:44, Lance Yang wrote: > From: Lance Yang > On Fri, 7 Nov 2025 17:59:22 +0800, Huacai Chen wrote: >> >> */ >> static inline pte_t *__pte_alloc_one_kernel_noprof(struct mm_struct *mm) >> { >> - struct ptdesc *ptdesc = pagetable_alloc_noprof(GFP_PGTABLE_KERNEL & >> - ~__GFP_HIGHMEM, 0); >> + struct ptdesc *ptdesc = pagetable_alloc_noprof(GFP_PGTABLE_KERNEL, 0); > > I looked into the history and it seems you are right. This defensive pattern > was likely introduced by Vishal Moola in commit c787ae5[1]. Right, so not even so long ago, so we need to make sure we agree on a direction and don't send opposite patches in the name of cleanups. > After this cleanup, would it make sense to add a BUILD_BUG_ON() somewhere > to check that __GFP_HIGHMEM is not present in GFP_PGTABLE_KERNEL and > GFP_PGTABLE_USER? This would prevent any future regression ;) > > Just a thought ... I think we can go either way here, but I'd tend towards not adding more checks but instead removing any mention of __GFP_HIGHMEM that we can show is either pointless or can be avoided, with the goal of having only a small number of actual highmem allocations remaining in places we do care about (normal page cache, zram, possibly huge pages). Arnd