[PATCH 2/3] mm: shmem: control THP support through the kernel command line

["Maíra Canal" <mcanal@igalia.com>]

Add a new kernel command line to control the hugepage allocation policy
for the internal shmem mount, ``transparent_hugepage_shmem``. The
parameter is similar to ``transparent_hugepage`` and has the following
format:

transparent_hugepage_shmem=<policy>

where ``<policy>`` is one of the seven valid policies available for
shmem.

By configuring the default hugepage allocation policy for the internal
shmem mount, applications that use shmem, such as the DRM GEM objects,
can take advantage of mTHP before it's been configured through sysfs.

Signed-off-by: Maíra Canal <mcanal@igalia.com>
---
 .../admin-guide/kernel-parameters.txt         |  7 ++++
 Documentation/admin-guide/mm/transhuge.rst    |  6 +++
 mm/shmem.c                                    | 38 ++++++++++++++++++-
 3 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 1666576acc0e..acabb04d0dd4 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6926,6 +6926,13 @@
 			See Documentation/admin-guide/mm/transhuge.rst
 			for more details.
 
+	transparent_hugepage_shmem= [KNL]
+			Format: [always|within_size|advise|never|deny|force]
+			Can be used to control the hugepage allocation policy for
+			the internal shmem mount.
+			See Documentation/admin-guide/mm/transhuge.rst
+			for more details.
+
 	trusted.source=	[KEYS]
 			Format: <string>
 			This parameter identifies the trust source as a backend
diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index 745055c3dc09..9b5b02c4d1ab 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -326,6 +326,12 @@ PMD_ORDER THP policy will be overridden. If the policy for PMD_ORDER
 is not defined within a valid ``thp_anon``, its policy will default to
 ``never``.
 
+Similarly to ``transparent_hugepage``, you can control the hugepage
+allocation policy for the internal shmem mount by using the kernel parameter
+``transparent_hugepage_shmem=<policy>``, where ``<policy>`` is one of the
+seven valid policies for shmem (``always``, ``within_size``, ``advise``,
+``never``, ``deny``, and ``force``).
+
 Hugepages in tmpfs/shmem
 ========================
 
diff --git a/mm/shmem.c b/mm/shmem.c
index 44282a296c33..24cdeafd8260 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -582,7 +582,6 @@ static bool shmem_huge_global_enabled(struct inode *inode, pgoff_t index,
 	}
 }
 
-#if defined(CONFIG_SYSFS)
 static int shmem_parse_huge(const char *str)
 {
 	if (!strcmp(str, "never"))
@@ -599,7 +598,6 @@ static int shmem_parse_huge(const char *str)
 		return SHMEM_HUGE_FORCE;
 	return -EINVAL;
 }
-#endif
 
 #if defined(CONFIG_SYSFS) || defined(CONFIG_TMPFS)
 static const char *shmem_format_huge(int huge)
@@ -5174,6 +5172,42 @@ struct kobj_attribute thpsize_shmem_enabled_attr =
 	__ATTR(shmem_enabled, 0644, thpsize_shmem_enabled_show, thpsize_shmem_enabled_store);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE && CONFIG_SYSFS */
 
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE)
+
+static int __init setup_transparent_hugepage_shmem(char *str)
+{
+	int huge, ret = 0;
+
+	if (!str)
+		goto out;
+
+	huge = shmem_parse_huge(str);
+	if (huge == -EINVAL)
+		goto out;
+
+	if (!has_transparent_hugepage() &&
+			huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/* Do not override huge allocation policy with non-PMD sized mTHP */
+	if (huge == SHMEM_HUGE_FORCE &&
+	    huge_shmem_orders_inherit != BIT(HPAGE_PMD_ORDER)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	shmem_huge = huge;
+	return 1;
+out:
+	pr_warn("transparent_hugepage_shmem= cannot parse, ignored\n");
+	return ret;
+}
+__setup("transparent_hugepage_shmem=", setup_transparent_hugepage_shmem);
+
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
 #else /* !CONFIG_SHMEM */
 
 /*
-- 
2.46.2