From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-111.freemail.mail.aliyun.com (out30-111.freemail.mail.aliyun.com [115.124.30.111]) (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 DD87B221FDE; Fri, 27 Mar 2026 13:45:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.111 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774619113; cv=none; b=iut5/SD5Qw8jkvXtz0o09FRLXdHezSHo2Y6HgJQO8ES6+pRSmXf2jMcuK7k//zKjU41c9CgtyfwakO3Y6fgnxOiVHn0yEPzZ5ZB7n7At4W3yNzIiCGqJiadf/y9x19LMjUDfchHWjvF8nF1S2agEz1K3iiParxPJp/xkjrls2+8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774619113; c=relaxed/simple; bh=dQ5yeCu+XRggWfYvMHL3f4uBspLzLrnyG1E50eBFPfw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=KLGRuD0NEUfNPEuxAdz9GdlZD5VPtWu6T8nK3uQb1FJ/CZdJ72i9zwI2jc/LCBRGQZtzM0hgP+TixJyFaAjwU1YXrLKe0k+9z9ZoG2DeR0/rmbG4HiONLS/uw2JkAAeLibLy+8QieIo75P7AZce5/RMtndwbYEqsPySewTnv9wI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=R1VVK0Og; arc=none smtp.client-ip=115.124.30.111 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="R1VVK0Og" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1774619106; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=DbLmVGzsI4+uNyjVzgEOD2NfpFFBuqWmyl7ZIzmxZec=; b=R1VVK0Og6Aga5K/4z682Re7Zwz8CLs8wR26E0l/v3vjxTH8hCADUEPzEWcCPEc77fty+Ja+2ouCqkOq+ybYlMtx36qU6+RuEjCuyUaZaGWSAJZ+jNamS78qOUr8Zjd3cCm/a0ZHcwy0rvkBD59cKcKHfaC5QyOpgxSaSqfTFjeY= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R191e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037009110;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=27;SR=0;TI=SMTPD_---0X.oRvWO_1774619103; Received: from 30.42.98.36(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X.oRvWO_1774619103 cluster:ay36) by smtp.aliyun-inc.com; Fri, 27 Mar 2026 21:45:04 +0800 Message-ID: Date: Fri, 27 Mar 2026 21:45:03 +0800 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 02/10] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check To: "Lorenzo Stoakes (Oracle)" Cc: Zi Yan , "Matthew Wilcox (Oracle)" , Song Liu , Chris Mason , David Sterba , Alexander Viro , Christian Brauner , Jan Kara , Andrew Morton , David Hildenbrand , "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 References: <20260327014255.2058916-1-ziy@nvidia.com> <20260327014255.2058916-3-ziy@nvidia.com> <7fd90f5e-65b5-4734-abb2-77b22c733af5@linux.alibaba.com> <8f5119a1-9aa9-4a39-ac94-ca1631db26e1@lucifer.local> From: Baolin Wang In-Reply-To: <8f5119a1-9aa9-4a39-ac94-ca1631db26e1@lucifer.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 3/27/26 8:02 PM, Lorenzo Stoakes (Oracle) wrote: > On Fri, Mar 27, 2026 at 05:44:49PM +0800, Baolin Wang wrote: >> >> >> On 3/27/26 9:42 AM, 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 */ >>> + if (mapping_max_folio_order(mapping) < PMD_ORDER) >>> + return SCAN_FAIL; >> >> This is not true for anonymous shmem, since its large order allocation logic >> is similar to anonymous memory. That means it will not call >> mapping_set_large_folios() for anonymous shmem. >> >> So I think the check should be: >> >> if (!is_shmem && mapping_max_folio_order(mapping) < PMD_ORDER) >> return SCAN_FAIL; > > Hmm but in shmem_init() we have: > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > if (has_transparent_hugepage() && shmem_huge > SHMEM_HUGE_DENY) > SHMEM_SB(shm_mnt->mnt_sb)->huge = shmem_huge; > else > shmem_huge = SHMEM_HUGE_NEVER; /* just in case it was patched */ > > /* > * Default to setting PMD-sized THP to inherit the global setting and > * disable all other multi-size THPs. > */ > if (!shmem_orders_configured) > huge_shmem_orders_inherit = BIT(HPAGE_PMD_ORDER); > #endif > > And shm_mnt->mnt_sb is the superblock used for anon shmem. Also > shmem_enabled_store() updates that if necessary. > > So we're still fine right? > > __shmem_file_setup() (used for anon shmem) calls shmem_get_inode() -> > __shmem_get_inode() which has: > > if (sbinfo->huge) > mapping_set_large_folios(inode->i_mapping); > > Shared for both anon shmem and tmpfs-style shmem. > > So I think it's fine as-is. I'm afraid not. Sorry, I should have been clearer. First, anonymous shmem large order allocation is dynamically controlled via the global interface (/sys/kernel/mm/transparent_hugepage/shmem_enabled) and the mTHP interfaces (/sys/kernel/mm/transparent_hugepage/hugepages-*kB/shmem_enabled). This means that during anonymous shmem initialization, these interfaces might be set to 'never'. so it will not call mapping_set_large_folios() because sbinfo->huge is 'SHMEM_HUGE_NEVER'. Even if shmem large order allocation is subsequently enabled via the interfaces, __shmem_file_setup -> mapping_set_large_folios() is not called again. Anonymous shmem behaves similarly to anonymous pages: it is controlled by the 'shmem_enabled' interfaces and uses shmem_allowable_huge_orders() to check for allowed large orders, rather than relying on mapping_max_folio_order(). The mapping_max_folio_order() is intended to control large page allocation only for tmpfs mounts. Therefore, I find the current code confusing and think it needs to be fixed: /* Don't consider 'deny' for emergencies and 'force' for testing */ if (sb != shm_mnt->mnt_sb && sbinfo->huge) mapping_set_large_folios(inode->i_mapping);