From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 2A6AF50EC0C; Mon, 7 Sep 2026 16:14:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788797663; cv=none; b=V5KnSXN5CidNReDDepnvRKRDfz/hetnJaNPuU7+p5IZKe8ZRlcVkXTMeWtCD2Y10/D6Eh4M/bAI+bgCCOmgRuVjRVRXuLaoh/RP1MxoDBASHsaRlS+cLymhQOxfWVMpvqEfM79vu24WGI24tyxDbx0X9sCtVq+JMrqrI2dnn+2A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788797663; c=relaxed/simple; bh=18Vzyhi2f55L/r/a4UKGHbp2A9qHgo+gHRb0i4enSw0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=m1vFbzfh7vMsWEHqYHBAyhtYBRkfR5gbGzzAGx1HHi5u3P0iQsYpckxEzRhy5vYuuw+pqnHH814HGu29p7XWlpdtP3NdEQiUzSnGCn6zLMcx+K26SBqroY+3pn9tm9y6OYSpMiulH4sNclZrHDCy1tJk8auowK5m90rBe5C44Bc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IVG4/GHp; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="IVG4/GHp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6DE941F00A3A; Mon, 7 Sep 2026 16:14:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788797661; bh=WgI0iNBWchDmZzxLFmjvIjEn2+5Z7VoBkjhiPKThMfo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=IVG4/GHpPL+vUHOsMFCbXNOtuArwUxJ7rkzHCjn7QDiJc9Gz6rUAweiF7wF1fdRpx KhHEy+kiH0FVQDhvBiP5GzDuwcMYUMJH7QTcYUjXResiYUY8+uvYR2X5du/sHumjXu u1MEx9cvejvr+bdZvq9A4JYCK4QYRs3lRQXrJ7eSQUO66tuJ5/EUZ8KmwAy54ucfs3 d7LgWbwHQ09Pz7tiwCOcix+ULPYANt547byrTXZAXbTOZuUabGCg4cebE3pOydMddR 8zAMek+qTfZuRLeepe06Gf3smUrZ4NbQZziZlV98RctqlRYt56RN0x423jp8XhjSJf rVHVKKWKknG7g== Message-ID: <034a2687-3551-485a-a382-e7e77aa3919b@kernel.org> Date: Mon, 7 Sep 2026 18:14:14 +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] mm/huge_memory: bypass THP tuneables for huge pfnmap mappings To: "Lorenzo Stoakes (ARM)" , Andrew Morton , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Peter Xu , Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Cedric Le Goater , Saravanan D , stable@vger.kernel.org References: <20260827-hugepfn-allowable-orders-v1-1-94819c8807c8@kernel.org> 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: <20260827-hugepfn-allowable-orders-v1-1-94819c8807c8@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/27/26 21:55, Lorenzo Stoakes (ARM) wrote: > The sysfs THP tuneables at /sys/kernel/mm/transparent_huge_pages/ rather > confusingly only control the behaviour of THP in some instances. > > They are not applicable to MADV_COLLAPSE operations, nor to DAX mappings. > > Long-term, THP is predicated upon compaction being able to obtain large > folios to populate THP ranges. > > However, vm_normal_folio() returns NULL for PFN map mappings, thus their > reference count is maintained by the driver, not core mm. > > As a consequence, the folios are not subject to reclaim nor compaction, so > are not truly part of the THP mechanism at all. > > However, since commit 5dd40721f147 ("mm: allow THP orders for PFNMAPs") > introduced the ability to establish huge PFN maps, they have been subject > to THP tuneables. > > This is incorrect - if a huge PFN map is available (defined by > vma->vm_ops->huge_fault being non-NULL for a VMA_PFNMAP_BIT VMA), then it > should be mapped huge upon fault-in. > > Correct this by explicitly checking for this while ensuring that smaps > continues to accurately report THPeligible statistics. > > While here, abstract the entire file-backed THP check in > vma_can_map_huge_file(), with sensible separation of logic into helper > functions. > > Note that drm_gem_shmem_mmap() and panthor_gem_mmap() establish huge PFN > maps of shmem folios, however they are marked unevictable in > drm_gem_get_pages(), and in any case would fail the reference check in > __remove_mapping() even if they weren't. > > Failing to map huge PFN maps has resulted in significant real-world > performance degradation, see links for details. > > Reported-by: Cedric Le Goater > Closes: https://lore.kernel.org/linux-mm/20260805055544.1568534-1-clg@redhat.com/ > Reported-by: Saravanan D > Closes: https://lore.kernel.org/linux-mm/20260821070520.25759-1-saravanand@crusoe.ai/ > Fixes: 5dd40721f147 ("mm: allow THP orders for PFNMAPs") > Cc: stable@vger.kernel.org > Signed-off-by: Lorenzo Stoakes (ARM) > --- > mm/huge_memory.c | 86 +++++++++++++++++++++++++++++++++++++++++--------------- > 1 file changed, 64 insertions(+), 22 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index afbb5974bd22..4bf7b670586d 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -92,7 +92,7 @@ unsigned long huge_anon_orders_madvise __read_mostly; > unsigned long huge_anon_orders_inherit __read_mostly; > static bool anon_orders_configured __initdata; > > -static inline bool file_thp_enabled(struct vm_area_struct *vma) > +static inline bool file_thp_enabled(const struct vm_area_struct *vma) > { > struct inode *inode; > > @@ -118,6 +118,67 @@ static bool vma_is_special_huge(const struct vm_area_struct *vma) > return vma_test_any(vma, VMA_PFNMAP_BIT, VMA_MIXEDMAP_BIT); > } > > +static bool vma_bypass_thp_tuneables_file(const struct vm_area_struct *vma, > + enum tva_type type) > +{ > + const bool has_huge_fault = vma->vm_ops->huge_fault; > + > + /* MADV_COLLAPSE ignores tuneables. */ > + if (type == TVA_FORCED_COLLAPSE) > + return true; > + /* Huge PFN mappings are uncompactable so the policy doesn't apply. */ > + if (vma_test(vma, VMA_PFNMAP_BIT) && has_huge_fault) > + return true; > + return false; > +} > + > +static bool vma_thp_tuneables_allow_file(vm_flags_t vm_flags) > +{ > + /* THP=always? */ > + if (hugepage_global_always()) > + return true; > + /* THP=madvise and marked MADV_HUGEPAGE? */ > + if (hugepage_global_enabled() && (vm_flags & VM_HUGEPAGE)) > + return true; > + return false; > +} > + > +static bool vma_check_thp_tuneables_file(const struct vm_area_struct *vma, > + vm_flags_t vm_flags, enum tva_type type) > +{ > + return vma_bypass_thp_tuneables_file(vma, type) || > + vma_thp_tuneables_allow_file(vm_flags); > +} > + > +static bool vma_can_map_huge_file(const struct vm_area_struct *vma, > + vm_flags_t vm_flags, enum tva_type type) > +{ > + const bool has_huge_fault = vma->vm_ops->huge_fault; > + > + /* > + * Enforce THP collapse requirements as necessary. Anonymous vmas > + * were already handled in thp_vma_allowable_orders(). > + */ > + if (!vma_check_thp_tuneables_file(vma, vm_flags, type)) > + return false; > + > + switch (type) { > + case TVA_PAGEFAULT: > + /* > + * Trust that ->huge_fault() handlers know what they are doing > + * in fault path. > + */ > + return has_huge_fault; > + case TVA_SMAPS: > + if (has_huge_fault) > + return true; > + fallthrough; > + default: > + /* Only regular file is valid in collapse path. */ > + return file_thp_enabled(vma); > + } > +} > + > unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > vm_flags_t vm_flags, > enum tva_type type, > @@ -190,27 +251,8 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > vma, vma_start_pgoff(vma), 0, > forced_collapse); > > - if (!vma_is_anonymous(vma)) { > - /* > - * Enforce THP collapse requirements as necessary. Anonymous vmas > - * were already handled in thp_vma_allowable_orders(). > - */ > - if (!forced_collapse && > - (!hugepage_global_enabled() || (!(vm_flags & VM_HUGEPAGE) && > - !hugepage_global_always()))) > - return 0; > - > - /* > - * Trust that ->huge_fault() handlers know what they are doing > - * in fault path. > - */ > - if (((in_pf || smaps)) && vma->vm_ops->huge_fault) > - return orders; > - /* Only regular file is valid in collapse path */ > - if (((!in_pf || smaps)) && file_thp_enabled(vma)) > - return orders; > - return 0; > - } > + if (!vma_is_anonymous(vma)) > + return vma_can_map_huge_file(vma, vm_flags, type) ? orders : 0; I don't have the time to find out how these functions ended up being named, I'll have to trust that it will be alright. Adding to what Zi say, vma_can_map_huge_file is also confusing, no? are we mapping a huge file? :) -- Cheers, David