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 8DDCC451069 for ; Wed, 13 May 2026 15:58:30 +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=1778687910; cv=none; b=DZ0XFGQQwXVkIcUslQfVWy4C87rg/MJCsqRcTBM2z9CaYhNBt6eZHzUsix3taCOiyDIgwty2FW7Cn4tyyr0szkSB9dqSF8z+zYqhCDhEFaFDSN847w81Lz3VSlanyJZ+zUfJf6pjqs8NwYWlFANaAIEb/UPt6BP+oK1S9jtPz64= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778687910; c=relaxed/simple; bh=PApq724J+inHsh/m+vC3mHQi47+Gf6kA+K/X2UX9bPM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fwOj4ictnlA6RhLX0HRxuwwg4oGoWKkUolLumo8r1Xt5zLw/BpSskVlKpNVcwfOvL7BGwjDwm7zGgVnk+RkjkdkjQom85X1JcfssUTrSvaVjZRumKvdZx9QaPtk+8ftmqPlUMIpVIbbvlty9EHbA45KHm9MEpbtNUeJBhTU16xo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dKPdBHzg; 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="dKPdBHzg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A8DE7C19425; Wed, 13 May 2026 15:58:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778687910; bh=PApq724J+inHsh/m+vC3mHQi47+Gf6kA+K/X2UX9bPM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=dKPdBHzggy1jv2nLtIFJzrbMfMvFdRtzQjfjx3v2I5hYGntW/mQ56NO4UHf79ixeq Ru3LDhIFJEOZdun9JTZ5Jsg3cGaJdw0xPGFHEBqWG2/02nnwzDQX3zTHD6lr0yOJNG 0h8uCZ8fwWPYAa49l6CVHltoAAFPFDX21YNvckPVns2algAidXm1KZlbbO8L++bvjd iEtiyProkaSekvq81bKZ9EguFu5whLLfqyHl3/oZIUkKNp++fedZrZGkjJY+MsM8U4 bDLDRjcPEm7k8H2msYAzgWkUB7XtFdz6Pfrvt4Kafw2x75p8ENk6EuKX1BiG2ACrM5 Xw4kEAi9nIlPg== Message-ID: Date: Wed, 13 May 2026 17:58:21 +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 v4 9/9] mm: thp: always enable mTHP support To: Luiz Capitulino , linux-kernel@vger.kernel.org, linux-mm@kvack.org, baolin.wang@linux.alibaba.com, ziy@nvidia.com, lance.yang@linux.dev Cc: corbet@lwn.net, tsbogend@alpha.franken.de, maddy@linux.ibm.com, mpe@ellerman.id.au, agordeev@linux.ibm.com, gerald.schaefer@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, x86@kernel.org, dave.hansen@linux.intel.com, djbw@kernel.org, vishal.l.verma@intel.com, dave.jiang@intel.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com References: From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/1/26 21:18, Luiz Capitulino wrote: > If PMD-sized pages are not supported on an architecture (ie. the > arch implements arch_has_pmd_leaves() and it returns false) then the > current code disables all THP, including mTHP. > > This commit fixes this by allowing mTHP to be always enabled for all > archs. When PMD-sized pages are not supported, its sysfs entry won't be > created and their mapping will be disallowed at page-fault time. > > Similarly, this commit implements the following changes for shmem in > shmem_allowable_huge_orders(): > > - Drop the pgtable_has_pmd_leaves() check so that mTHP sizes are > considered > - Filter out PMD and PUD orders from allowable orders when > PMD-sized pages are not supported by the CPU > > Signed-off-by: Luiz Capitulino > --- > mm/huge_memory.c | 23 ++++++++++++++++++----- > mm/shmem.c | 14 +++++++++----- > 2 files changed, 27 insertions(+), 10 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 32254febe097..c1765c8e3dc6 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -126,6 +126,14 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > else > supported_orders = THP_ORDERS_ALL_FILE_DEFAULT; > > + if (!pgtable_has_pmd_leaves()) { > + /* > + * The CPU doesn't support PMD-sized pages, assume it > + * doesn't support PUD-sized pages either. > + */ I'd say here "If the CPU does not support PMD leaves, assume for now that it does not support PUD leaves and disable both folio orders." > + supported_orders &= ~(BIT(PMD_ORDER) | BIT(PUD_ORDER)); > + } > + > orders &= supported_orders; > if (!orders) > return 0; > @@ -133,7 +141,7 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > if (!vma->vm_mm) /* vdso */ > return 0; > > - if (!pgtable_has_pmd_leaves() || vma_thp_disabled(vma, vm_flags, forced_collapse)) > + if (vma_thp_disabled(vma, vm_flags, forced_collapse)) > return 0; > > /* khugepaged doesn't collapse DAX vma, but page fault is fine. */ > @@ -848,7 +856,7 @@ static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj) > * disable all other sizes. powerpc's PMD_ORDER isn't a compile-time > * constant so we have to do this here. > */ > - if (!anon_orders_configured) > + if (!anon_orders_configured && pgtable_has_pmd_leaves()) > huge_anon_orders_inherit = BIT(PMD_ORDER); > > *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj); > @@ -870,6 +878,14 @@ static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj) > } > > orders = THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_FILE_DEFAULT; > + if (!pgtable_has_pmd_leaves()) { > + /* > + * The CPU doesn't support PMD-sized pages, assume it > + * doesn't support PUD-sized pages either. > + */ > + orders &= ~(BIT(PMD_ORDER) | BIT(PUD_ORDER)); > + } > + > order = highest_order(orders); > while (orders) { > thpsize = thpsize_create(order, *hugepage_kobj); > @@ -969,9 +985,6 @@ static int __init hugepage_init(void) > int err; > struct kobject *hugepage_kobj; > > - if (!pgtable_has_pmd_leaves()) > - return -EINVAL; > - > /* > * hugepages can't be allocated by the buddy allocator > */ > diff --git a/mm/shmem.c b/mm/shmem.c > index a48f034830cd..23893c2bc2dd 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1840,16 +1840,19 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode, > unsigned long mask = READ_ONCE(huge_shmem_orders_always); > unsigned long within_size_orders = READ_ONCE(huge_shmem_orders_within_size); > vm_flags_t vm_flags = vma ? vma->vm_flags : 0; > - unsigned int global_orders; > + unsigned int global_orders, filter_orders = 0; > > - if (!pgtable_has_pmd_leaves() || (vma && vma_thp_disabled(vma, vm_flags, shmem_huge_force))) > + if (vma && vma_thp_disabled(vma, vm_flags, shmem_huge_force)) > return 0; > > + if (!pgtable_has_pmd_leaves()) > + filter_orders = BIT(PMD_ORDER) | BIT(PUD_ORDER); Would "disabled_orders" or "unavailable_orders" be more appropriate? There is no need to disable PUD-orders, as shmem does not support PUD-orders (unlike DAX). So you can keep it simpler here. > + > global_orders = shmem_huge_global_enabled(inode, index, write_end, > shmem_huge_force, vma, vm_flags); > /* Tmpfs huge pages allocation */ > if (!vma || !vma_is_anon_shmem(vma)) > - return global_orders; > + return global_orders & ~filter_orders; > > /* > * Following the 'deny' semantics of the top level, force the huge > @@ -1863,7 +1866,7 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode, > * means non-PMD sized THP can not override 'huge' mount option now. > */ > if (shmem_huge == SHMEM_HUGE_FORCE) > - return READ_ONCE(huge_shmem_orders_inherit); > + return READ_ONCE(huge_shmem_orders_inherit) & ~filter_orders; > > /* Allow mTHP that will be fully within i_size. */ > mask |= shmem_get_orders_within_size(inode, within_size_orders, index, 0); > @@ -1874,6 +1877,7 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode, > if (global_orders > 0) > mask |= READ_ONCE(huge_shmem_orders_inherit); > > + mask &= ~filter_orders; > return THP_ORDERS_ALL_FILE_DEFAULT & mask; > } > > @@ -5457,7 +5461,7 @@ void __init shmem_init(void) > * Default to setting PMD-sized THP to inherit the global setting and > * disable all other multi-size THPs. > */ > - if (!shmem_orders_configured) > + if (!shmem_orders_configured && pgtable_has_pmd_leaves()) > huge_shmem_orders_inherit = BIT(HPAGE_PMD_ORDER); Do we really want to change that? We can just leave the defaults as is, no? -- Cheers, David