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Mon, 21 Sep 2026 10:29:18 +0000 X-Mizu-Trace-ID: 58aaa6d2d129fc08 X-Migadu-Flow: FLOW_OUT From: Usama Arif To: Luiz Capitulino Cc: Usama Arif , linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org, baolin.wang@linux.alibaba.com, ziy@nvidia.com, lance.yang@linux.dev, 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, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, hughd@google.com, dave.hansen@linux.intel.com, djbw@kernel.org, vishal.l.verma@intel.com, dave.jiang@intel.com, akpm@linux-foundation.org, yintirui@huawei.com, dev.jain@arm.com Subject: Re: [PATCH v8 14/14] mm: thp: always enable mTHP support Date: Mon, 21 Sep 2026 03:29:12 -0700 Message-ID: <20260921102913.2970139-1-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <752f528f0fed5cdc9de12b54260b0495d4e5a6cb.1789695931.git.luizcap@redhat.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 314A2C0008 X-Stat-Signature: qyb345yr4px9nuht3i3bijiqoyzoampf X-Rspam-User: X-HE-Tag: 1789986561-853687 X-HE-Meta: U2FsdGVkX1/KBH9/s4sFvMQfrR1CRRW/EG5DmsPJKsMNiRgDe1xdbwvyN/tYzTo8XjfD9VoTUiZvP7nP4XfMFD6gQuRcnkr5vPuW2YzrOmt+g/YkMaztO8QF5cnQC5XYtJapjHrM9uLe7VfgGTC3p6cJxOuxpw50St97vYoPeG1uKyHD3r6C9ZPvVc7BZUz+PPSy8qRj0TW9u0TRlkCW4W/YP2v0dDsRxVJq2mDO1+jtsEDTfxD9/3G5RSTFY0vd314IInbe7kBjcM0ueMwtPsqkvdGMLT3arfg0dOKRi+eDetFSRLZPa5J9jsmvjgKQr7W1+FMctZr12DuqiKnQjeUJ6/DeTeN9CzC/PZQ1i8TJxV/g81ZPSbkB8o4Knzkbj1Yfz1W6ku2tnnNmJ9axPYYM4VGmcgp3x1mNZCELiWaddgQX/rNmbXuqC5prs/3ULVhr8SWgWFHCMYZ+rkJuOZy65UThyfBqdbiLie+T60D53t4X80x9IQfkweIi2CkraWKvgkIdF8eUc0tNhD/F8Rh+aN727VaeUuFgWqpe0IK6TE/PzgkBdHeg+hMWGlxvNOtNkp93BnacX1Xk2NaLWpCCnAE6MPuJTzHa5LIjlvdXYGckGBElul0zC0b4g2lP2e52T1Y/uMH5j+I5/uEHvU5EZ2q0F4WI4uBdXb3tK9HHW+LBmAqig/Y6lESZwjgky0pJ6YQj4txBo7v4bLNXiA1pr8kvuRC15CHvuLFqhkV/S0Qsb0mnv1Npyf/M3P068mOyH4HiXmNiDzwVHe+9xSrYz8eNnLBnGZ7Z/0i5ANYfKxXjwDcsPMY567+HKEEpwc556nq4ZgxXYHTjeQm3EYoZ+wPCW2NkAmntdyisW4J3/U4QImc4xW0f3k12XGG7EE6cnpywec2XuD5YCkgsMcnZq3l3DXVmnBkvN3zAeNkhsMIkBEjZ8XSuhudkJVwWRGKBNr90ZA3yETx8DLc xUU+xXzH Y6kwtkUTuftkDdSt3OCTtFaxGGtCtZ9PI0tRkEqXYVyAE6YvyVtiBryzgPR9W48Nj99K6nXePK2pUJN7jve6aInB665pzp91SPLR8CaLY89XnUpEtu1cQcIb/P+hjc++BuL1QLA8YOzqDoL2uDG+pQGIUJhOXJUbBRTqzoa6z9id/U4EFoCr3ubOhcDXZiUpz5V1mSvBEoh5mygV+VvdTK2J/PCglGZxwp9Utzbs/D58dFr6vMr+9tX+1mtsWytiquLbD Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 17 Sep 2026 21:45:35 -0400 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 | 25 ++++++++++++++++++++----- > mm/shmem.c | 14 +++++++++----- > 2 files changed, 29 insertions(+), 10 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index a06025b87e7c..a2d6de3ea988 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -189,6 +189,15 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > else > supported_orders = THP_ORDERS_ALL_FILE_DEFAULT; > > + if (!pgtable_has_pmd_leaves()) { > + /* > + * 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; > @@ -196,7 +205,7 @@ 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. */ > @@ -979,7 +988,7 @@ 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); > @@ -1001,6 +1010,15 @@ 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()) { > + /* > + * If the CPU does not support PMD leaves, assume for > + * now that it does not support PUD leaves and disable > + * both folio orders. > + */ > + orders &= ~(BIT(PMD_ORDER) | BIT(PUD_ORDER)); > + } > + > order = highest_order(orders); > while (orders) { > thpsize = thpsize_create(order, *hugepage_kobj); > @@ -1091,9 +1109,6 @@ static int __init hugepage_init(void) > int err; > struct kobject *hugepage_kobj; > > - if (!pgtable_has_pmd_leaves()) > - return -EINVAL; > - Removing this guard lets start_stop_khugepaged() run on a system without PMD leaves. All mTHP orders default to never, but the global always or madvise flag still makes hugepage_enabled() return true. That starts an idle khugepaged thread and can unnecessarily raise min_free_kbytes. Could hugepage_enabled() instead test whether an enabled order remains after masking PMD_ORDER when pgtable_has_pmd_leaves() is false? > /* > * hugepages can't be allocated by the buddy allocator > */ > diff --git a/mm/shmem.c b/mm/shmem.c > index bc2de3a7c1ea..8c0f7e3efeeb 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -2046,11 +2046,14 @@ 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, disabled_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()) > + disabled_orders = BIT(PMD_ORDER); > + > global_orders = shmem_huge_global_enabled(inode, index, write_end, > shmem_huge_force, vma, vm_flags); > /* > @@ -2058,7 +2061,7 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode, > * sysfs configs. > */ > if (!vma || !vma_is_anon_shmem(vma) || shmem_huge_force) > - return global_orders; > + return global_orders & ~disabled_orders; > > /* > * Following the 'deny' semantics of the top level, force the huge > @@ -2072,7 +2075,7 @@ 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) & ~disabled_orders; > > /* Allow mTHP that will be fully within i_size. */ > mask |= shmem_get_orders_within_size(inode, within_size_orders, index, 0); > @@ -2083,6 +2086,7 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode, > if (global_orders > 0) > mask |= READ_ONCE(huge_shmem_orders_inherit); > > + mask &= ~disabled_orders; > return THP_ORDERS_ALL_FILE_DEFAULT & mask; > } > > @@ -5630,7 +5634,7 @@ 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); > #endif > return; > -- > 2.55.0 > >