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 C816C10ED64A for ; Fri, 27 Mar 2026 12:07:28 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 159A46B0092; Fri, 27 Mar 2026 08:07:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 131E76B0095; Fri, 27 Mar 2026 08:07:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0470D6B0098; Fri, 27 Mar 2026 08:07:27 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id E66216B0092 for ; Fri, 27 Mar 2026 08:07:27 -0400 (EDT) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 9B417E0FC5 for ; Fri, 27 Mar 2026 12:07:27 +0000 (UTC) X-FDA: 84591718134.19.73D67C4 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf04.hostedemail.com (Postfix) with ESMTP id DF04140009 for ; Fri, 27 Mar 2026 12:07:25 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="GV/OuxUv"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf04.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1774613246; a=rsa-sha256; cv=none; b=VX9z/8P+empxP1eJhEz7QxFpphViNi+nzvW1IZCiP9UvJjqbTpIZ/lJkIONus/I9HF0cGR xg9RiBBPrE6pmaYkuuAMMrf0jy+XJaaE8OboEN5Gl9T9I2KCrqKZvv/q5Uu9Qb/gyW8IhH pi4XM7beGBGEZv7gdojcMpDrzCdVsS8= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="GV/OuxUv"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf04.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1774613246; 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=pmqgFpm73FDUUHz6djr/tPqUzEHt4kZKcDr9Hf18iQU=; b=1FsK52mj8Xx3om95DpNjN+BBHsuK8Ha4EXzqfgtLhWvJJ0wrfbcViigWIvSuPTWQj+VpqW 0GIVgFTkdLbVnfH7Vw2H8jBLcmm8GJx93/WFZF+/7eV412mr/2/6ihdAVenmwx9uj1yTnP WKPHytJ/9md7uQA7u6vUCSWc3fkOSkE= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id B1F2340DAC; Fri, 27 Mar 2026 12:07:24 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 000F7C19423; Fri, 27 Mar 2026 12:07:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774613244; bh=2nB5DCPY0+8yCmvF7X6fCAPWRpuyi5kzCg7/hMaBpWM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=GV/OuxUvODHLD58X/NXS2HIl2fDAtcrOkYl1usoY5dT3mhOCLFz+yYGOP1vLLqYOU 15w99o49viWVLThwMVhKQQ4mpejWHKm/7mtnHk603YlQMPyZeiGUpI1aYuUMTC1qoK KP9QBrIxE8qH4usannUbPyhHkjf13t9L/naWuMmlMqpNeQm5IoyhpmO87gPoLqBf38 FLBh1X6kvQW7NNnskhElLwD+CVW0SDGiuK3j+25mlnqfgSphcqJQtpx/983A9czRbG 4lwP0/0dPbdKzGiM8hrNqbD6znlN6oHLzNcQqRNhGxdV9U8tI0Q7kPFORW+bOdT5XM WrZvcbArOiAzg== Date: Fri, 27 Mar 2026 12:07:22 +0000 From: "Lorenzo Stoakes (Oracle)" To: Zi Yan Cc: "Matthew Wilcox (Oracle)" , Song Liu , Chris Mason , David Sterba , Alexander Viro , Christian Brauner , Jan Kara , Andrew Morton , David Hildenbrand , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v1 02/10] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check Message-ID: <31d9d5c1-02af-42b3-bc3e-aea151d3552b@lucifer.local> References: <20260327014255.2058916-1-ziy@nvidia.com> <20260327014255.2058916-3-ziy@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260327014255.2058916-3-ziy@nvidia.com> X-Stat-Signature: uakqxj1bsqgtpk5wbzmm6uf6yb1crea3 X-Rspamd-Queue-Id: DF04140009 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1774613245-252499 X-HE-Meta: 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 nTIiNzc2 ctCwFyCRbmuWcYUIYSjQTKbosbquae+tw+cFUidvdQyL/tbyt5ZSvmhZjE3K83qu8ISEvkDtlTrHhOMMbHVkprHp+wwS8xq7uyAhCOQNy6LCJ3uawp2p+7gOmwPsvdHUHwBBaLr2BmGPEvHSvcM+nSU2ASd9JaVNZLdcnoJCzn8z0j0zx0udCoR/vk+Z2xD1u3WNghKmk4Z7mRhZtWphtB4vZbgyCa15sBQaX10tXG2OkiZeSNtR+w7V1MfkFGVNQzDSIKtT7LHrWiV972ico/gIDIPFH3utqnF+6 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Mar 26, 2026 at 09:42:47PM -0400, Zi Yan wrote: > collapse_file() requires FSes supporting large folio with at least > PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that. shmem with > huge option turned on also sets large folio order on mapping, so the check > also applies to shmem. > > While at it, replace VM_BUG_ON with returning failure values. > > Signed-off-by: Zi Yan > --- > mm/khugepaged.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index d06d84219e1b..45b12ffb1550 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1899,8 +1899,11 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, > int nr_none = 0; > bool is_shmem = shmem_file(file); > > - VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem); > - VM_BUG_ON(start & (HPAGE_PMD_NR - 1)); > + /* "huge" shmem sets mapping folio order and passes the check below */ I think this isn't quite clear and could be improved to e.g.: /* * Either anon shmem supports huge pages as set by shmem_enabled sysfs, * or a shmem file system mounted with the "huge" option. */ > + if (mapping_max_folio_order(mapping) < PMD_ORDER) > + return SCAN_FAIL; As per rest of thread, this looks correct. > + if (start & (HPAGE_PMD_NR - 1)) > + return SCAN_ADDRESS_RANGE; Hmm, we're kinda making this - presumably buggy situation - into a valid input that just fails the scan. Maybe just make it a VM_WARN_ON_ONCE()? Or if we want to avoid propagating the bug that'd cause it any further: if (start & (HPAGE_PMD_NR - 1)) { VM_WARN_ON_ONCE(true); return SCAN_ADDRESS_RANGE; } Or similar. > > result = alloc_charge_folio(&new_folio, mm, cc); > if (result != SCAN_SUCCEED) > -- > 2.43.0 > Cheers, Lorenzo