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Tue, 10 Feb 2026 05:28:27 -0800 (PST) Received: from [192.168.2.110] ([76.65.77.217]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8caf9fdfa1bsm1047769185a.45.2026.02.10.05.28.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Feb 2026 05:28:27 -0800 (PST) Message-ID: <0c0886d5-2561-40e4-94e9-6fca15f25127@redhat.com> Date: Tue, 10 Feb 2026 08:28:16 -0500 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 v2 10/11] mm: thp: always enable mTHP support To: Baolin Wang , linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org Cc: ryan.roberts@arm.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com References: <29e8dfc2772af4b6e0db24134ca3563ec422b91a.1770675272.git.luizcap@redhat.com> Content-Language: en-US, en-CA From: Luiz Capitulino In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2026-02-10 04:56, Baolin Wang wrote: > > > On 2/10/26 6:14 AM, 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 >> - In shmem_alloc_and_add_folio(): don't consider PMD and PUD orders >> when PMD-sized pages are not supported by the CPU >> >> Signed-off-by: Luiz Capitulino >> --- >> mm/huge_memory.c | 11 +++++++---- >> mm/shmem.c | 4 +++- >> 2 files changed, 10 insertions(+), 5 deletions(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 1e5ea2e47f79..882331592928 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -115,6 +115,9 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, >> else >> supported_orders = THP_ORDERS_ALL_FILE_DEFAULT; >> + if (!pgtable_has_pmd_leaves()) >> + supported_orders &= ~(BIT(PMD_ORDER) | BIT(PUD_ORDER)); >> + >> orders &= supported_orders; >> if (!orders) >> return 0; >> @@ -122,7 +125,7 @@ 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. */ >> @@ -806,6 +809,9 @@ 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()) >> + orders &= ~(BIT(PMD_ORDER) | BIT(PUD_ORDER)); > > I think you should also handle the 'huge_anon_orders_inherit' setting in this function if pgtable_has_pmd_leaves() returns false. Shmem as well. > > if (!anon_orders_configured) > huge_anon_orders_inherit = BIT(PMD_ORDER); Good catch. So, would you agree that should set it to BIT(PMD_ORDER - 1) in this case? > >> + >> order = highest_order(orders); >> while (orders) { >> thpsize = thpsize_create(order, *hugepage_kobj); >> @@ -905,9 +911,6 @@ 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 1c98e84667a4..cb325d1e2d1e 100644 >> --- a/mm/shmem.c >> +++ b/mm/shmem.c >> @@ -1827,7 +1827,7 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode, >> vm_flags_t vm_flags = vma ? vma->vm_flags : 0; >> unsigned int global_orders; >> - 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; >> global_orders = shmem_huge_global_enabled(inode, index, write_end, >> @@ -1935,6 +1935,8 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf, >> if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) >> orders = 0; >> + else if (!pgtable_has_pmd_leaves()) >> + orders &= ~(BIT(PMD_ORDER) | BIT(PUD_ORDER)); > > Moving this check into shmem_allowable_huge_orders() would be more appropriate. Will do. Thanks a lot for the very fast review. > >> if (orders > 0) { >> suitable_orders = shmem_suitable_orders(inode, vmf, >