[RFC PATCH v1 3/4] mm: Override mTHP "enabled" defaults at kernel cmdline

[Ryan Roberts]

Add thp_anon= cmdline parameter to allow specifying the default
enablement of each supported anon THP size. The parameter accepts the
following format and can be provided multiple times to configure each
size:

thp_anon=<size>[KMG]:<value>

See Documentation/admin-guide/mm/transhuge.rst for more details.

Configuring the defaults at boot time is useful to allow early user
space to take advantage of mTHP before its been configured through
sysfs.

Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
---
 .../admin-guide/kernel-parameters.txt         |  8 +++
 Documentation/admin-guide/mm/transhuge.rst    | 26 +++++++--
 mm/huge_memory.c                              | 55 ++++++++++++++++++-
 3 files changed, 82 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index bc55fb55cd26..48443ad12e3f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6592,6 +6592,14 @@
 			<deci-seconds>: poll all this frequency
 			0: no polling (default)
 
+	thp_anon=	[KNL]
+			Format: <size>[KMG]:always|madvise|never|inherit
+			Can be used to control the default behavior of the
+			system with respect to anonymous transparent hugepages.
+			Can be used multiple times for multiple anon THP sizes.
+			See Documentation/admin-guide/mm/transhuge.rst for more
+			details.
+
 	threadirqs	[KNL,EARLY]
 			Force threading of all interrupt handlers except those
 			marked explicitly IRQF_NO_THREAD.
diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index 1aaf8e3a0b5a..f53d43d986e2 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -311,13 +311,27 @@ performance.
 Note that any changes to the allowed set of sizes only applies to future
 file-backed THP allocations.
 
-Boot parameter
-==============
+Boot parameters
+===============
 
-You can change the sysfs boot time defaults of Transparent Hugepage
-Support by passing the parameter ``transparent_hugepage=always`` or
-``transparent_hugepage=madvise`` or ``transparent_hugepage=never``
-to the kernel command line.
+You can change the sysfs boot time default for the top-level "enabled"
+control by passing the parameter ``transparent_hugepage=always`` or
+``transparent_hugepage=madvise`` or ``transparent_hugepage=never`` to the
+kernel command line.
+
+Alternatively, each supported anonymous THP size can be controlled by
+passing ``thp_anon=<size>[KMG]:<state>``, where ``<size>`` is the THP size
+and ``<state>`` is one of ``always``, ``madvise``, ``never`` or
+``inherit``.
+
+For example, the following will set 64K THP to ``always``::
+
+	thp_anon=64K:always
+
+``thp_anon=`` may be specified multiple times to configure all THP sizes as
+required. If ``thp_anon=`` is specified at least once, any anon THP sizes
+not explicitly configured on the command line are implicitly set to
+``never``.
 
 Hugepages in tmpfs/shmem
 ========================
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 4249c0bc9388..794d2790d90d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -82,6 +82,7 @@ unsigned long huge_anon_orders_madvise __read_mostly;
 unsigned long huge_anon_orders_inherit __read_mostly;
 unsigned long huge_file_orders_always __read_mostly;
 int huge_file_exec_order __read_mostly = -1;
+static bool anon_orders_configured;
 
 unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
 					 unsigned long vm_flags,
@@ -763,7 +764,10 @@ 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.
 	 */
-	huge_anon_orders_inherit = BIT(PMD_ORDER);
+	if (!anon_orders_configured) {
+		huge_anon_orders_inherit = BIT(PMD_ORDER);
+		anon_orders_configured = true;
+	}
 
 	/*
 	 * For pagecache, default to enabling all orders. powerpc's PMD_ORDER
@@ -955,6 +959,55 @@ static int __init setup_transparent_hugepage(char *str)
 }
 __setup("transparent_hugepage=", setup_transparent_hugepage);
 
+static int __init setup_thp_anon(char *str)
+{
+	unsigned long size;
+	char *state;
+	int order;
+	int ret = 0;
+
+	if (!str)
+		goto out;
+
+	size = (unsigned long)memparse(str, &state);
+	order = ilog2(size >> PAGE_SHIFT);
+	if (*state != ':' || !is_power_of_2(size) || size <= PAGE_SIZE ||
+	    !(BIT(order) & THP_ORDERS_ALL_ANON))
+		goto out;
+
+	state++;
+
+	if (!strcmp(state, "always")) {
+		clear_bit(order, &huge_anon_orders_inherit);
+		clear_bit(order, &huge_anon_orders_madvise);
+		set_bit(order, &huge_anon_orders_always);
+		ret = 1;
+	} else if (!strcmp(state, "inherit")) {
+		clear_bit(order, &huge_anon_orders_always);
+		clear_bit(order, &huge_anon_orders_madvise);
+		set_bit(order, &huge_anon_orders_inherit);
+		ret = 1;
+	} else if (!strcmp(state, "madvise")) {
+		clear_bit(order, &huge_anon_orders_always);
+		clear_bit(order, &huge_anon_orders_inherit);
+		set_bit(order, &huge_anon_orders_madvise);
+		ret = 1;
+	} else if (!strcmp(state, "never")) {
+		clear_bit(order, &huge_anon_orders_always);
+		clear_bit(order, &huge_anon_orders_inherit);
+		clear_bit(order, &huge_anon_orders_madvise);
+		ret = 1;
+	}
+
+	if (ret)
+		anon_orders_configured = true;
+out:
+	if (!ret)
+		pr_warn("thp_anon=%s: cannot parse, ignored\n", str);
+	return ret;
+}
+__setup("thp_anon=", setup_thp_anon);
+
 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 {
 	if (likely(vma->vm_flags & VM_WRITE))
-- 
2.43.0