mm: shmem: control THP support through the kernel command line

Patch series "mm: add more kernel parameters to control mTHP", v5.

This series introduces four patches related to the kernel parameters
controlling mTHP and a fifth patch replacing `strcpy()` for `strscpy()` in
the file `mm/huge_memory.c`.

The first patch is a straightforward documentation update, correcting the
format of the kernel parameter ``thp_anon=``.

The second, third, and fourth patches focus on controlling THP support for
shmem via the kernel command line.  The second patch introduces a
parameter to control the global default huge page allocation policy for
the internal shmem mount.  The third patch moves a piece of code to a
shared header to ease the implementation of the fourth patch.  Finally,
the fourth patch implements a parameter similar to ``thp_anon=``, but for
shmem.

The goal of these changes is to simplify the configuration of systems that
rely on mTHP support for shmem.  For instance, a platform with a GPU that
benefits from huge pages may want to enable huge pages for shmem.  Having
these kernel parameters streamlines the configuration process and ensures
consistency across setups.


This patch (of 4):

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.

Configuring the default huge page allocation policy for the internal
shmem mount can be beneficial for DRM GPU drivers. Just as CPU
architectures, GPUs can also take advantage of huge pages, but this is
possible only if DRM GEM objects are backed by huge pages.

Since GEM uses shmem to allocate anonymous pageable memory, having control
over the default huge page allocation policy allows for the exploration of
huge pages use on GPUs that rely on GEM objects backed by shmem.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Maíra Canal <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Barry Song <[email protected]>
Cc: [email protected]
Cc: Hugh Dickins <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: [email protected]
Cc: Lance Yang <[email protected]>
Cc: Ryan Roberts <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: mairacanal

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

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
 ========================
 

mm/shmem.c

@@ -582,24 +582,39 @@ static bool shmem_huge_global_enabled(struct inode *inode, pgoff_t index,
 	}
 }
 
-#if defined(CONFIG_SYSFS)
 static int shmem_parse_huge(const char *str)
 {
+	int huge;
+
+	if (!str)
+		return -EINVAL;
+
 	if (!strcmp(str, "never"))
-		return SHMEM_HUGE_NEVER;
-	if (!strcmp(str, "always"))
-		return SHMEM_HUGE_ALWAYS;
-	if (!strcmp(str, "within_size"))
-		return SHMEM_HUGE_WITHIN_SIZE;
-	if (!strcmp(str, "advise"))
-		return SHMEM_HUGE_ADVISE;
-	if (!strcmp(str, "deny"))
-		return SHMEM_HUGE_DENY;
-	if (!strcmp(str, "force"))
-		return SHMEM_HUGE_FORCE;
-	return -EINVAL;
+		huge = SHMEM_HUGE_NEVER;
+	else if (!strcmp(str, "always"))
+		huge = SHMEM_HUGE_ALWAYS;
+	else if (!strcmp(str, "within_size"))
+		huge = SHMEM_HUGE_WITHIN_SIZE;
+	else if (!strcmp(str, "advise"))
+		huge = SHMEM_HUGE_ADVISE;
+	else if (!strcmp(str, "deny"))
+		huge = SHMEM_HUGE_DENY;
+	else if (!strcmp(str, "force"))
+		huge = SHMEM_HUGE_FORCE;
+	else
+		return -EINVAL;
+
+	if (!has_transparent_hugepage() &&
+	    huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY)
+		return -EINVAL;
+
+	/* Do not override huge allocation policy with non-PMD sized mTHP */
+	if (huge == SHMEM_HUGE_FORCE &&
+	    huge_shmem_orders_inherit != BIT(HPAGE_PMD_ORDER))
+		return -EINVAL;
+
+	return huge;
 }
-#endif
 
 #if defined(CONFIG_SYSFS) || defined(CONFIG_TMPFS)
 static const char *shmem_format_huge(int huge)
@@ -5065,15 +5080,7 @@ static ssize_t shmem_enabled_store(struct kobject *kobj,
 
 	huge = shmem_parse_huge(tmp);
 	if (huge == -EINVAL)
-		return -EINVAL;
-	if (!has_transparent_hugepage() &&
-			huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY)
-		return -EINVAL;
-
-	/* Do not override huge allocation policy with non-PMD sized mTHP */
-	if (huge == SHMEM_HUGE_FORCE &&
-	    huge_shmem_orders_inherit != BIT(HPAGE_PMD_ORDER))
-		return -EINVAL;
+		return huge;
 
 	shmem_huge = huge;
 	if (shmem_huge > SHMEM_HUGE_DENY)
@@ -5170,6 +5177,25 @@ 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;
+
+	huge = shmem_parse_huge(str);
+	if (huge == -EINVAL) {
+		pr_warn("transparent_hugepage_shmem= cannot parse, ignored\n");
+		return huge;
+	}
+
+	shmem_huge = huge;
+	return 1;
+}
+__setup("transparent_hugepage_shmem=", setup_transparent_hugepage_shmem);
+
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
 #else /* !CONFIG_SHMEM */
 
 /*