[PATCH v2 4/5] mm: shmem: add a kernel command line to change the default huge policy for tmpfs

[Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>]

Now the tmpfs can allow to allocate any sized large folios, and the default
huge policy is still 'never'. Thus adding a new command line to change
the default huge policy will be helpful to use the large folios for tmpfs,
which is similar to the 'transparent_hugepage_shmem' cmdline for shmem.

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
 .../admin-guide/kernel-parameters.txt         |  7 ++++++
 Documentation/admin-guide/mm/transhuge.rst    |  6 +++++
 mm/shmem.c                                    | 23 ++++++++++++++++++-
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b48d744d99b0..007e6cfada3e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6943,6 +6943,13 @@
 			See Documentation/admin-guide/mm/transhuge.rst
 			for more details.
 
+	transparent_hugepage_tmpfs= [KNL]
+			Format: [always|within_size|advise|never]
+			Can be used to control the default hugepage allocation policy
+			for the tmpfs 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 5034915f4e8e..9ae775eaacbe 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -332,6 +332,12 @@ allocation policy for the internal shmem mount by using the kernel parameter
 seven valid policies for shmem (``always``, ``within_size``, ``advise``,
 ``never``, ``deny``, and ``force``).
 
+Similarly to ``transparent_hugepage_shmem``, you can control the default
+hugepage allocation policy for the tmpfs mount by using the kernel parameter
+``transparent_hugepage_tmpfs=<policy>``, where ``<policy>`` is one of the
+four valid policies for tmpfs (``always``, ``within_size``, ``advise``,
+``never``). The tmpfs mount default policy is ``never``.
+
 In the same manner as ``thp_anon`` controls each supported anonymous THP
 size, ``thp_shmem`` controls each supported shmem THP size. ``thp_shmem``
 has the same format as ``thp_anon``, but also supports the policy
diff --git a/mm/shmem.c b/mm/shmem.c
index a3203cf8860f..021760e91cea 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -548,6 +548,7 @@ static bool shmem_confirm_swap(struct address_space *mapping,
 /* ifdef here to avoid bloating shmem.o when not necessary */
 
 static int shmem_huge __read_mostly = SHMEM_HUGE_NEVER;
+static int tmpfs_huge __read_mostly = SHMEM_HUGE_NEVER;
 
 /**
  * shmem_mapping_size_orders - Get allowable folio orders for the given file size.
@@ -4780,7 +4781,12 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
 	sbinfo->gid = ctx->gid;
 	sbinfo->full_inums = ctx->full_inums;
 	sbinfo->mode = ctx->mode;
-	sbinfo->huge = ctx->huge;
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	if (ctx->seen & SHMEM_SEEN_HUGE)
+		sbinfo->huge = ctx->huge;
+	else
+		sbinfo->huge = tmpfs_huge;
+#endif
 	sbinfo->mpol = ctx->mpol;
 	ctx->mpol = NULL;
 
@@ -5259,6 +5265,21 @@ static int __init setup_transparent_hugepage_shmem(char *str)
 }
 __setup("transparent_hugepage_shmem=", setup_transparent_hugepage_shmem);
 
+static int __init setup_transparent_hugepage_tmpfs(char *str)
+{
+	int huge;
+
+	huge = shmem_parse_huge(str);
+	if (huge < 0) {
+		pr_warn("transparent_hugepage_tmpfs= cannot parse, ignored\n");
+		return huge;
+	}
+
+	tmpfs_huge = huge;
+	return 1;
+}
+__setup("transparent_hugepage_tmpfs=", setup_transparent_hugepage_tmpfs);
+
 static char str_dup[PAGE_SIZE] __initdata;
 static int __init setup_thp_shmem(char *str)
 {
-- 
2.39.3