From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0AD15354AFF for ; Mon, 2 Feb 2026 09:06:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770023183; cv=none; b=VsecI0fOGjSO6NfderZATsM3Tdz6xPnE4+PPB38I55jxowPlf+tsR0wYPe/Xsu5iKrn0MasR914gp1Ac7YgCGlnGTK5KNiWO8mmyJ005xlJhv9kNTasPCKjertXLjFuyzBZ46N5zkFBWO0l2gw6vQsYXe54we1bjUSmlS7IU+o4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770023183; c=relaxed/simple; bh=fo6NhVGIQqemKxe9ZZvK/jM3T+1bXA+BAOzWhjoeDDA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=DX6+8ZKWKhAPdA9xj3sG14h5qOFKGhSMmM8WKR7jmxEIFTHNV8EoFpUgU7GcXMEM04KUBQrgD82H1maqUBaktjsh3qXXYQRHngnSl8Lyq2zJwWBCop++5voV/ZrswxZcUWoKANtj7J9jOpydHueJvLPBt1THtOeN8lK0KEKFYII= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Z6Sej69s; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Z6Sej69s" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E406EC116D0; Mon, 2 Feb 2026 09:06:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770023182; bh=fo6NhVGIQqemKxe9ZZvK/jM3T+1bXA+BAOzWhjoeDDA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Z6Sej69s+w0LKQ7FeIhvn14r/S0dGDexKBfNsmeHk3uxLqUHNGoQ6kEIkr0h4oZwc Pyf4oI0ugpOf2JX5nNqZX8924gTOz0R1RuYxvGlOI3V0fqwunYaWtV2Rlw8TxJ5xBg y17ILG1K8GAvIQPs57v5vZcnHibO9/Rw+1y3RLcvseydilQELD0QTxYztH5pK050Pf uY6Msd30koKvgN2IqgDJowVjzlIEVSqxVWYFAtepjM8Eh/au41QpmBbuwHj7EtLKwX A+jAXKPhbbIFfcAxcXuY0wRdFxqlHn9C1bNpr7pFSre12YGPIvJrv1ODSabL4/UtIv 5Jdc4GtLF6jug== Message-ID: <7d6f5fd3-9652-4e9d-89af-e81ce20df8ba@kernel.org> Date: Mon, 2 Feb 2026 10:06:14 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 00/12] mm: PUD (1GB) THP implementation To: Matthew Wilcox , Usama Arif Cc: ziy@nvidia.com, Andrew Morton , lorenzo.stoakes@oracle.com, linux-mm@kvack.org, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, npache@redhat.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, vbabka@suse.cz, lance.yang@linux.dev, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20260202005451.774496-1-usamaarif642@gmail.com> From: "David Hildenbrand (arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/2/26 05:00, Matthew Wilcox wrote: > On Sun, Feb 01, 2026 at 04:50:17PM -0800, Usama Arif wrote: >> This is an RFC series to implement 1GB PUD-level THPs, allowing >> applications to benefit from reduced TLB pressure without requiring >> hugetlbfs. The patches are based on top of >> f9b74c13b773b7c7e4920d7bc214ea3d5f37b422 from mm-stable (6.19-rc6). > > I suggest this has not had enough testing. There are dozens of places > in the MM which assume that if a folio is at leaast PMD size then it is > exactly PMD size. Everywhere that calls folio_test_pmd_mappable() needs > to be audited to make sure that it will work properly if the folio is > larger than PMD size. I think the hack (ehm trick) in this patch set is to do it just like dax PUDs: only map through a PUD or through PTEs, not through PMDs. That also avoids dealing with mapcounts until I sorted that out. -- Cheers David