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 8EC5433DED5 for ; Tue, 12 May 2026 07:51:29 +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=1778572289; cv=none; b=OSNVwIYmtRH7X1I8oTvDlWwI6igbLk+tGJ+BHorGkxZySOXsCqQ8i4BNKAeSaApf41zCnnTKEyvOWZrq7x0uuqj+74PCBxtLJRjz7NOGklTiiHDOXNFwhaWGahCMUfqAkqL56nsdmlaKiQ1BU4gVTO6dAlpjra5g8hGBXDemCII= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778572289; c=relaxed/simple; bh=Dq8ING+5fXzkYw+tuaMqTiP1VzJarHzMr6tQqmPU8dc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Fed3D4JuMWmfDPam+JwkhqwohHTgEPhwzH16gddUX3T4NbLkJV3sgln0s2c6PEMIwoy5BgRu6dAJF7/jSRbM7ZSMhSuXQsZbvS0Qa33Zi3j40ZHd8N0nscNpcOYLI/8hsXrZI5vSWvI8dyoLsFIprN8675y5R2fuxknusSKGVjc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Tsb6Mhn5; 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="Tsb6Mhn5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9FECDC2BCB8; Tue, 12 May 2026 07:51:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778572289; bh=Dq8ING+5fXzkYw+tuaMqTiP1VzJarHzMr6tQqmPU8dc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Tsb6Mhn5W7yHRlJBXykDzeOXgNLdHkKpj0ScceVhTJeGMjwpRaTOu/XBHC5j7/ANp dxH0KoykFdSUCnu9PvxPRfj5amBhduE+D+qptUCZFhlAytu2VhMQ8Q5ucxis9Jj7pN b0yWyz5/X1rDdWboculE//6uVUVqoEREQy7plO7Vz8E4wQkdE6iiEAqoeclt17uO29 L4hF0xUH7Z+fU+Je+2ZdOUT+MFGjVL+ol60h7zDbmwx+eoZOOB15rxGXClEBMWkAJp 42XtgqxHF9BJs4mjc15p2ogvnzDJJfd+dY1GemoudCAhZOnkHBJtAGyrDXuqvwKFhD D17DnqiaryqUQ== Message-ID: <8ef6e92d-4cb3-444e-857e-fdbf88c035ea@kernel.org> Date: Tue, 12 May 2026 09:51:05 +0200 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: "alloc_tag was not set" when running mm/ksft_hmm.sh To: Alistair Popple Cc: Zenghui Yu , Zenghui Yu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, jgg@ziepe.ca, leon@kernel.org, Andrew Morton , ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com References: <10e4565a-b416-45d9-a8b0-cd32532b2630@kernel.org> <2b46241c-158b-c9dd-9b81-a98366b2c9fb@huawei.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 5/12/26 09:46, Alistair Popple wrote: > On 2026-05-12 at 16:47 +1000, "David Hildenbrand (Arm)" wrote... >> On 5/12/26 03:28, Alistair Popple wrote: >>> On 2026-05-12 at 02:38 +1000, Zenghui Yu wrote... >>> >>> Thanks. I have reproduced it now that my fingers are skinnier. >>> >>> >>> Well you know what they say about assumptions :) Although in this case >>> __folio_freeze_and_split_unmapped() isn't called on the backing page anyway >>> (it's called to split the ZONE_DEVICE page, not the page simulating device >>> memory). >> >> Now my brain hurts :) > > I have never liked this bit of the HMM selftests. It has always made my brain > hurt. > >>> The problem is we're not splitting the tag associated with the backing >>> page for the simulated memory. >>> >>> I came up with the below fix last night, but I suspect it will quite reasonably >>> get NACKED on the basis of the symbol export so was looking at other solutions. >> >> I think there are other problems ... >> >>> >>> The simulated memory should just be used like a bare physical address range. So >>> there really is no reason for the backing page simulating device memory to be >>> allocated as a higher order folio. Using the struct page to store some metadata >>> for the simulated device is convenient though to avoid creating a test-specific >>> data structure for this. So I am looking at going back to allocating the >>> simulated backing memory as always order-0 pages in the test which is what it >>> was prior to the introduction of large device pages, but that was causing a >>> crash I'm yet to debug. >>> >> >> ... such as doing a folio_page(folio_alloc()), followed by a __free_pages(). >> >> Why are we even allocating folios here and manually splitting them? >> >> Looking at dmirror_devmem_folio_split(), aren't we using folios here for >> something that ... is not a folio? >> >> Likely we really shouldn't be using folios here ... :) > > Exactly my point, just more succinct :) > > I just need to make it work without doing that. Ok, great. You could also allocate a larger buddy page and just split it manually through split_page. split_page will even do the pgalloc_tag_split :) -- Cheers, David