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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=PsJ8kMUS; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 87020606A31C; Thu, 12 Nov 2026 08:41:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=PsJ8kMUS Received: by smtp.kernel.org (Postfix) with ESMTPSA id CAB6A1F00A05; Thu, 12 Nov 2026 08:41:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794472864; bh=fthYHrOF+5dGTgn8Y4kE22m9q7Cd14oHg/PsNYTRC5E=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=PsJ8kMUSB3EGJHW5qVwks6Qbwv20bXjnqIFTIR1/ceR+LGf0okaQt5ej3o6UnAG9b NgCUKP1pJLcvkSnD6BTPbnRvYTZ6/dU4ahXisnoyn+tMutkCXjlfuWiil8rMgs30tE XdrjWQQgBiuz56RgSslBx2lTpeu0Z/yvVpB7hAJu67AyrU6+0bPx986QjCpCaY4lmS I8XJG8lbO5ethYZ4njetFgkB1YksOYlFQMwHOTo/Gxi1cvuS38g4iPYz+DJurvIy/D 63hkpRkD9PzX8UJ+4XXJk9KARRtMb3MnFtGpt/bBkqjViDzamXuN+9TuRQnl9HuflR AHJnt9MR5zn8w== Message-ID: <8712ee27-85b0-4342-a3f5-7e9b4425b804@kernel.org> Date: Thu, 12 Nov 2026 09:40:57 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/3] mm: gup: allow long-term pins of CMA-allocated HugeTLB folios To: Qi Zheng , muchun.song@linux.dev, osalvador@suse.de, akpm@linux-foundation.org, azpijr@gmail.com, lance.yang@linux.dev, Qi Zheng Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org References: <586d6c53ab7e4c64d6e89ad3cf0cf7e07dabbfaf.1794046188.git.zhengqi.arch@bytedance.com> <7abb3aa1-385a-422f-86bd-7aac9661c4d8@kernel.org> <423c9b28-ecf2-4fab-817d-2fb326690c73@linux.dev> <3a1a3bb5-0b01-4f20-aa0e-74a952544b8c@kernel.org> <5f68ffba-9f56-4e31-9e7c-9d110f552efc@bytedance.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/11/26 11:26, Qi Zheng wrote: > Hi David, > > On 11/11/26 3:43 PM, David Hildenbrand (Arm) wrote: >> On 11/9/26 04:10, Qi Zheng wrote: >>> >>> >>> >> >> You resent your series way too fast. > > Got it. > >> >> Now we have discussions in to threads, congratulations ;) >> >>> ;), got it. >>> >>> I moved the code to resolve a build dependency. >>> >> >> Why can't that be resolved differently? What is the dependency? > > The dependency is that the new check wants to use > `folio_test_hugetlb_cma()`, which is a HugeTLB-specific inline helper > from `include/linux/hugetlb.h`. > > `folio_is_longterm_pinnable()` currently lives in `include/linux/mm.h`, > while `include/linux/hugetlb.h` already includes `linux/mm.h`. So I > can't simply use `folio_test_hugetlb_cma()` from `mm.h` It's all so hacky. :) core-mm shouldn't have to worry about hugetlb internals like folio_test_hugetlb_cma(). >>> >>> A generic query may need separate ownership tracking, such as an >>> owned_bitmap recording successfully allocated pages. Its updates and >>> lookups would also need to handle concurrency with fast GUP. >> >> Or simply two bitmaps? "trying allocation - allocated" > > As a fix, perhaps this is a bit too complex? :( > > Alternatively, we could adjust the timing for setting the bitmap, though > this might introduce new concurrency issues. I think we had that order reversed in the past. Likely a second bitmap would allow us to fix it fairly easily. -- Cheers, David