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 2E72B384CEF for ; Tue, 12 May 2026 06:47:55 +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=1778568476; cv=none; b=hjjulBcCqNdwzFv7h+yvEsDQuQFI36MyVTMrPnbJs0+hy9ITEzLKbQpUG4JpsKZZMiiec8AZQdhCr7QNyDmgGqRmvGn3tVKQxJrcwGWhx0JSo3wCygzPcV3avwXCKEpqEivY3nnWeuhzt+Cvi+vC426zSSQnccxYjOBi3rnTMU8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778568476; c=relaxed/simple; bh=znb+tX+r6T235ZS5HNLK+QxawBsaGf/IdcCTZMqLRqA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=MNir8P/70aLAEfusZzjLoMzuFvMidiK+APcRcoLLL+8OVnv5g92xIvLU+e/DpLLR2JYvt+V/dG1fl5UjBFWCY0624I/euVtYOYWDd8vWf2US9ZIBHUXGJdKejlPxBL5doxxWRykr7gm4F5ohC7YwilHEcHz/iJDfKywGZX0DPU8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Y+Vq/+kn; 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="Y+Vq/+kn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7EA01C2BCFA; Tue, 12 May 2026 06:47:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778568474; bh=znb+tX+r6T235ZS5HNLK+QxawBsaGf/IdcCTZMqLRqA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Y+Vq/+knyZI4VnnF4ShT+GGtlQMb3D2bGKxc8fSm27jU7wVLLsruEkfmsGoGukU3A pr9bNxaDsYx8Q61wwldFLMUV2owW66wuz1pa9C4YmtwNof4Etd1KvZO2HxObq7iufu gnYr2+cXjig7nuPPG97J6Xtvfw5YoEAMsggfdeI10fMJ3tMtbvt0Gme3zGHU2vNTnU XlxWGAP0M/mJPqtrExlAnkeczmER+kz8VuKgTh6V9CaBX8LdjYhTDinBnO19+mzXi+ /omcduC71RkDXFwzkYhs7+KBCwuDmOVvO9ulPNEQ2XHQ9eENh+pKB7NWlY4VCe7c5y YMlm2U2X4nFaQ== Message-ID: Date: Tue, 12 May 2026 08:47:49 +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 , Zenghui Yu Cc: 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 03:28, Alistair Popple wrote: > On 2026-05-12 at 02:38 +1000, Zenghui Yu wrote... >> Hi David, >> >> On 5/11/26 8:47 PM, David Hildenbrand (Arm) wrote: > > Thanks. I have reproduced it now that my fingers are skinnier. > >>> >>> >>> zone_device_private_split_cb(), that ends up calling ->folio_split(). >>> >>> We do have a call to pgalloc_tag_split() in __split_unmapped_folio(), invoked in >>> __folio_freeze_and_split_unmapped() before calling >>> zone_device_private_split_cb() when iterating the folios. >> >> If I read the code correctly, pgalloc_tag_split() in >> __split_unmapped_folio() deals with device private pages' alloc tag. But >> what alloc_tag_sub_check() warns on are real system memory pages (device >> page's backing page), which are allocated by >> dmirror_devmem_alloc_page()/folio_page(). >> >> static void dmirror_devmem_folio_split(struct folio *head, struct folio >> *tail) >> { >> struct page *rpage = BACKING_PAGE(folio_page(head, 0)); >> >> Thanks, >> Zenghui >> >>> The zone_device_private_split_cb(folio, NULL); is then called on the first folio >>> after looping over the other (new) folios. >>> >>> I would assume that __folio_freeze_and_split_unmapped() would already do the >>> right thing? > > 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 :) > 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 ... :) -- Cheers, David