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[67.164.59.41]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7b0ccb5a517sm3354317b3a.57.2025.11.07.08.34.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Nov 2025 08:34:32 -0800 (PST) Date: Fri, 7 Nov 2025 08:34:29 -0800 From: "Vishal Moola (Oracle)" To: Arnd Bergmann Cc: Lance Yang , Huacai Chen , Andrew Morton , Huacai Chen , Jan Kara , Kevin Brodsky , Linux-Arch , linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org, Lorenzo Stoakes , Lance Yang Subject: Re: [PATCH Resend] mm: Refine __{pgd,p4d,pud,pmd,pte}_alloc_one_*() about HIGHMEM Message-ID: References: <20251107095922.3106390-1-chenhuacai@loongson.cn> <20251107114455.59111-1-ioworker0@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 97F1A180005 X-Stat-Signature: jskrgai4f9fzdr5xcdt6hf1k9bix9trm X-HE-Tag: 1762533274-73622 X-HE-Meta: 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 gm7DePD5 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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 Fri, Nov 07, 2025 at 01:50:06PM +0100, Arnd Bergmann wrote: > 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. I took a look, this patch is the direction we want to go :). > > 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 ... In this case, I don't think the extra check is necessary. This is a remnant of defensively converting callers to the ptdesc api from get_free_pages() variants (which masks off GFP_HIGHMEM internally). I doubt we'll ever be changing those macros to support highmem. > 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). +1 I'm not familiar with which architectures use highmem or not, so theres likely more cases like this patch that are remnants of the ptdesc conversion. git grep "pagetable_alloc.*GFP_HIGHMEM" shows at least 5 references inline that can definitely be removed. I'll go ahead and clean those up, but I'll leave the rest to people more familiar with the architectures.