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 C78403EDE71 for ; Wed, 13 May 2026 09:30:33 +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=1778664633; cv=none; b=KaRtDdX37kXoF1sNV/HZizqFjwg5akl89UoG0PW589M2VASAUWVuYmjMnUA2c+PlcUyJPcWLQcr03ldnMzM2L93hmEGkO+4LzQAHfjHG8SxK6NwmsxVFKs3gj1sx+6BpP9XgT0PgBrzJSJY6ovBzYXktO6zfqwdzGPPnvWprw6Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778664633; c=relaxed/simple; bh=jqpWcTvsVENQMjHz/cvx8R37HUe7D5wGYNm7WLuXu64=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LJBQzKcVfJEb4YUOyEBFXRyHZPw6gjBUTLiJOq5fZ/dHs6eFmOeE5849qg7yQzWp5kOthkPXpoLwvJQqGVvtWO4JlZoZqVbSsnytd1fclIwX7fi0+hzTjj9nlTA4EBBJjsaKiToV52hSRu+KmXtUSRwDn02LVqCQDpolyNlHBVE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=N+fkX5Hu; 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="N+fkX5Hu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 95BF4C2BCB8; Wed, 13 May 2026 09:30:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778664633; bh=jqpWcTvsVENQMjHz/cvx8R37HUe7D5wGYNm7WLuXu64=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=N+fkX5HuWU74GLq2SjvCq5yUEPpsyBsbrjcDBijXbdz/cVz7WKrvzEdJFKwbwx3Z4 s2OZyXU6O8g1bYpgFzglIUV2Q5Iqm7JMyKyhaHvUR3m1UaRDJNuattBlC9+w715ssT ynt8/BLUKAphUvaEaTK/DYTdjdJafyP3oM1H+aSiVSvfv4d9HTZeJkjg5ShrMm6mrn qJIZEFDOrNLN6y2AygIu8KkKNzdrxqiOQS+lg9Z+gp3tl08y/WVpYXGX5K8mScaLgm NuZ3thX/xIu8ckkfxEG1Nw2/dQsVntoH/tkoXKCt9xcdw/u85fHnro2s3361TZoS5T QBAAo75hHyYhw== Message-ID: <683399e9-eb3c-4aeb-ace3-670aa43247ed@kernel.org> Date: Wed, 13 May 2026 11:30:25 +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: [PATCH 1/2] mm/shmem: add shmem_insert_folio() To: =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , =?UTF-8?Q?Christian_K=C3=B6nig?= , intel-xe@lists.freedesktop.org Cc: Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Hugh Dickins , Baolin Wang , Brendan Jackman , Johannes Weiner , Zi Yan , Huang Rui , Matthew Auld , Matthew Brost , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260512110339.6244-1-thomas.hellstrom@linux.intel.com> <20260512110339.6244-2-thomas.hellstrom@linux.intel.com> <26479389-459b-4cc4-914d-e7d29d5e5cc9@kernel.org> <68705cec43ab43088327b21c9d9318036fb2a255.camel@linux.intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <68705cec43ab43088327b21c9d9318036fb2a255.camel@linux.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi, >> >> Yeah but that is the requirement the HW has. >> >> I mean we can keep torturing the buddy allocator to give us 2M pages, >> but essentially we want to get away from those specialized solutions >> and has more of the functionality necessary to driver the HW in the >> common Linux memory management code because that prevents vendors >> from re-implementing that stuff in their specific driver over and >> over again. > > For the code at hand, if we insert an order 10 folio shmem will split > it at writeout time but spit out a warning (if enabled) at the same > time. For this particular use-case, I think it might make sense for the > drivers that use direct insertion to cap the page-allocator orders to > THP size (2M). I think this just points at the bigger problem: shmem should be allocating folios, not someone else on shmem's behalf. > >> >> Regards, >> Christian. >> >>> c) You pass folio + order, which is just the red flag that you are >>> doing >>>    something extremely dodgy. >>> >>>    You just cast something that is not a folio, and was not >>> allocated to be a >>>    folio to a folio through page_folio(page). That will stop >>> working completely >>>    in the future once we decouple struct page from struct folio. >>> >>>    If it's not a folio with a proper set order, you should be >>> passing page + >>>    order. >>> >>> d) We are once more open-coding creation of a folio, by hand- >>> crafting it >>>    ourselves. >>> >>>    We have folio_alloc() and friends for a reason. Where we, for >>> example, do a >>>    page_rmappable_folio(). >>> >>>    I am pretty sure that you are missing a call to >>> page_rmappable_folio(), >>>    resulting in the large folios not getting >>> folio_set_large_rmappable() set. >>> >>> e) undo_compound_page(). No words. >>> >>> >>> >>> *maybe* it would be a little less bad if you would just allocate a >>> compound page >>> in your driver and use page_rmappable_folio() in there. > > OK, yes it sounds like a prereq for this is that the driver actually > allocates compound pages. It might be that the TTM comment about *not* > doing that is stale, but need to check. > > Would it be acceptable to export a function from core mm to split an > isolated folio? The point is: an allocated page, including an allocated compound page, is logically not a folio. We have work going on to decouple both concepts completely. We do have functions to split folios. But it should be given a proper folio, not something that can currently be cast to a folio. > >>> >>> That wouldn't change a) or b), though. >>> >>> >>> >>> Good question. >>> We'd have to keep swapoff and all of that working. For example, in >>> try_to_unuse(), we special-case shmem_unuse() to handle non- >>> anonymous pages. >>> >>> But then, the whole swapcache operates on folios ... so I am not >>> sure if there >>> is a lot to be won by re-implementing what shmem already does? >>> > > Still that would alleviate a) and b), right? At least as long as we > keep folio sizes within the swap cache limits? Let's hear from Christian what would be required for DRM to use shmem natively. Maybe there would be a possible solution to have a custom shmem-like intnal thing that can better deal with large folios. -- Cheers, David