[PATCH v1 12/14] mm/mshare: Add a proc file with mshare alignment/size information

[Khalid Aziz <khalid.aziz@oracle.com>]

mshare regions are subject to size and alignment requirement. This
alignment boundary can be different on different architectures and
userspace needs a way to know what the requirement is. Add a file
/proc/sys/vm//mshare_size that can be read by userspace to get
the alignment and size requirement.

Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
---
v1:
	- Provide a way for userspace to determine alignment and
	  size retriction (based upon feedback from Dave Hansen)

 include/linux/mm.h | 1 +
 kernel/sysctl.c    | 7 +++++++
 mm/mshare.c        | 3 +++
 3 files changed, 11 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 821ed7ee7b41..d9456d424202 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3339,6 +3339,7 @@ unsigned long wp_shared_mapping_range(struct address_space *mapping,
 #endif
 
 extern int sysctl_nr_trim_pages;
+extern ulong sysctl_mshare_size;
 
 #ifdef CONFIG_PRINTK
 void mem_dump_obj(void *object);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 730ab56d9e92..66697ba5da88 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2810,6 +2810,13 @@ static struct ctl_table vm_table[] = {
 		.extra2		= SYSCTL_ONE,
 	},
 #endif
+	{
+		.procname	= "mshare_size",
+		.data		= &sysctl_mshare_size,
+		.maxlen		= sizeof(sysctl_mshare_size),
+		.mode		= 0444,
+		.proc_handler	= proc_doulongvec_minmax,
+	},
 	{ }
 };
 
diff --git a/mm/mshare.c b/mm/mshare.c
index ec23d1db79b2..88c7cefc933d 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -28,6 +28,8 @@ struct mshare_data {
 	refcount_t refcnt;
 };
 
+ulong sysctl_mshare_size;
+
 static struct super_block *msharefs_sb;
 
 /* Returns holding the host mm's lock for read.  Caller must release. */
@@ -573,6 +575,7 @@ mshare_init(void)
 	if (ret)
 		sysfs_remove_mount_point(fs_kobj, "mshare");
 
+	sysctl_mshare_size = PGDIR_SIZE;
 	return ret;
 }
 
-- 
2.32.0