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imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=dKPdBHzg; spf=pass (imf24.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1778687910; a=rsa-sha256; cv=none; b=g0J7Uj8BBCHOhr7C/t2NZOk+AZoWRFTr/aNVeYnr1SPmwsVXACIrfkpyIgfKb1IkWyz6Bb qlSS9gGMcD+BI0cAEYFlNP+IzKg+ddnZbW7ldnxo0f4dWCDfo9WrTJC7xpgJXpw5dwa2rs MN1iYqw3r3+RlzBFpgrrNWZu2ml7hVo= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 414B260126; Wed, 13 May 2026 15:58:30 +0000 (UTC) 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 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 X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: CE71418000D X-Rspam-User: X-Stat-Signature: auc64b4qd1j348r7enhh6t7gxpk5rwbz X-HE-Tag: 1778687910-193692 X-HE-Meta: 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 2vGFO/Y6 NVLac+s0DkOdigOTFlsIdAyqIAtEFyrDnYvwXF07IrYJwQT0pvSC053JROrKo/XXWYRyOSf8Q3/QD1PzP6Qm6WboEiZgzwZJ6bAPJOdCboYduo9fpTKyX2OPxRevYAahxgIMlMYATDrBzpOnS4mdMD6//bsYdt0jxMesCSY1ZisAoAEYoG3RUeRXj3k9uh2PSQWhPWIRj9Kd+datPOipaWDvhHuCTS7zZE9aZT8Y29n0yNNtWDs98b53EZ82FRtFNP4HMux8hGLSn7LlitlzAMOdFPw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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