From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 04110C5DF7D for ; Fri, 21 Aug 2026 08:03:27 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E09A56B008C; Fri, 21 Aug 2026 04:03:25 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DBB106B009D; Fri, 21 Aug 2026 04:03:25 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CD1126B00A0; Fri, 21 Aug 2026 04:03:25 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id A0CFF6B008C for ; Fri, 21 Aug 2026 04:03:25 -0400 (EDT) Received: from smtpin18.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 1DAEA1403AB for ; Fri, 21 Aug 2026 08:03:25 +0000 (UTC) X-FDA: 85124536770.18.D0802CC Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf27.hostedemail.com (Postfix) with ESMTP id 8B4134000C for ; Fri, 21 Aug 2026 08:03:23 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=aYXyUBvH; spf=pass (imf27.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1787299403; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Xl/eqcse8q01TGfMWGAYjBFpqsEhjPokKNvvi+tLs1Y=; b=Hth2rSl/Zgu8Iumwg9vm/O/lLb3PxrMbQpDuPQ77EwPB+pXDyHrybD9D1BwJMoT0gj4WVl 7WjwpynHq38WL8R0xw0UZuvYuyXiF6C27MVT16xsxJOIFyP92Wa+jIEVX9B8VE8+hQH5Kd 1BHuNcYpve/GV1wN8e0TJiKPuLoC/yk= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1787299403; b=LeNgt1rD0Qv7/qMY0fvZeKNl0MEFlN4fTb9pU6H4E9Fu/PHplrhwSoVpoS44EQG3Yd+/nR tkYvN+/KltSEC59TjVHSXpZDv4uPseu1kCQ1f+y5yT7pkVQRWQW2577dPsnviKjenFFqhX J8KWO/3PUEE+oc7e7v56wE0mysrPgM8= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=aYXyUBvH; spf=pass (imf27.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id CBCA160A77; Fri, 21 Aug 2026 08:03:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 73DAC1F000E9; Fri, 21 Aug 2026 08:03:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787299402; bh=Xl/eqcse8q01TGfMWGAYjBFpqsEhjPokKNvvi+tLs1Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=aYXyUBvHuWjxr5r5eke88584RfNeQiUv+Z11RSeOyKCJggIp2nOOOkrdSWdQub4Oo FEmsOg1wM0tLHoJClvfXiLGGTuPCPmlyT0ak6hbN/HUGcC409TYNT1hUMrU7+3CkbK oEV7YcB8aSyGuYu9ujOHDN/hxTNq20RrzZ+2vDp1M62m5veKaUf9wVdMhzcm9D/fHt IipPH+TMQDy/DeS/BGCKZ9euJ3ugymN70cPWTNl8Y3qBGrrhRBGgt7ltQqma7NKJGx BzbrDqjhhZyfMSZVPoqVEKP1dZdaVhqgwdNlgait2VYyzRfa34YE7PS0dhPzQDrcKf lG8NCr2eeNcIQ== Date: Fri, 21 Aug 2026 09:03:15 +0100 From: "Lorenzo Stoakes (ARM)" To: Saravanan D Cc: Andrew Morton , linux-mm@kvack.org, David Hildenbrand , Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Peter Xu , Alex Williamson , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/huge_memory: allow huge pfnmaps regardless of THP mode Message-ID: References: <20260821070520.25759-1-saravanand@crusoe.ai> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260821070520.25759-1-saravanand@crusoe.ai> X-Rspam-User: X-Stat-Signature: eq4skaaaaa3eqf6payk7q3jjtn4jtp7w X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 8B4134000C X-HE-Tag: 1787299403-777214 X-HE-Meta: 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 Z53DXhus TNf51gqDmlaCanAhGucFf3NSAJWLjtXYQQTz71qhjjbL/iJWpZhkh5pX0WXxfaBuKlRulIdNdfOImp1TD21mdqg5YZvve1AuL2OhgUv+XG7bnvWmk6964mAlq9V6g/T4zgQiVob2zmrux7K963a8v4G056wodCSWJfmh5D8XsNjh3S6pzRypUsC+iDSM2CiCecDhYEpMWoeSoMu1+9QKR4V4pTR5tMrBlgxQRvhfdc7SIwg6BrfewZXYd8oesc0uy7lM5hMdNl5sDbFwa0IZ5qyitZn5uYC6nJvUXyCSmpSTOLzawIGd3lq3X4/NLFTRiaUdt2Bx0d2D+DG89khy8VEen+rfeUQHvdpH252hhQosTHjt8uirjIxMV4w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Nope. On Fri, Aug 21, 2026 at 12:05:20AM -0700, Saravanan D wrote: > The THP mode check in __thp_vma_allowable_orders() runs before the > clause that trusts huge_fault() handlers, so huge pfnmaps only > materialize when THP is set to "always". The THP modes exist to > limit the memory and khugepaged costs of transparent hugepages. > Special mappings are backed by pfns instead of THP folios and > khugepaged never scans them, so those costs do not apply and we > can exempt special mappings from the mode check. This also makes > THPeligible in smaps report 1 for such mappings. > > This matters for VFIO device passthrough on distributions where > the default THP mode is "madvise". Mapping a 128 GiB GPU BAR > through VFIO_IOMMU_MAP_DMA costs 33.5 million order 0 faults and > 20.7 seconds when the mode denies huge pfnmaps. With huge pfnmaps > allowed, the same mapping takes 128 PUD faults and 0.4 seconds. > > Signed-off-by: Saravanan D This seems like AI slop. We don't want it, thanks. Read https://docs.kernel.org/process/coding-assistants.html and https://docs.kernel.org/process/generated-content.html and follow kernel guidelines please. In any case if you'd taken 5 minutes to search the mailing list you'd see this was: a. Already submitted (so your patch reads like plagiarism). b. Already rejected in favour of me doing an actually sensible solution. https://lore.kernel.org/linux-mm/anL-NZkNMSSxN0YN@lucifer/ > --- > mm/huge_memory.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index afbb5974bd22..bc61b8020af6 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -193,9 +193,10 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > if (!vma_is_anonymous(vma)) { > /* > * Enforce THP collapse requirements as necessary. Anonymous vmas > - * were already handled in thp_vma_allowable_orders(). > + * were already handled in thp_vma_allowable_orders(). Special > + * mappings have no THP costs and are exempt. > */ > - if (!forced_collapse && > + if (!forced_collapse && !vma_is_special_huge(vma) && > (!hugepage_global_enabled() || (!(vm_flags & VM_HUGEPAGE) && > !hugepage_global_always()))) > return 0; > > base-commit: a032d41a86cb82a747bc14d9c82b3e153a9a9ab7 > -- > 2.53.0 > -- Cheers, Lorenzo