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

Khalid Aziz
2022-04-11T16:09:49Z

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