[PATCH v3 3/3] shmem: Expose space and accounting error count

[Gabriel Krisman Bertazi <krisman@collabora.com>]

Exposing these shmem counters through sysfs is particularly useful for
container provisioning, to allow administrators to differentiate between
insufficiently provisioned fs size vs. running out of memory.

Suggested-by: Amir Goldstein <amir73il@gmail.com>
Suggested-by: Khazhy Kumykov <khazhy@google.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
---
 Documentation/ABI/testing/sysfs-fs-tmpfs | 13 ++++++++++++
 mm/shmem.c                               | 25 ++++++++++++++++++++++++
 2 files changed, 38 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-fs-tmpfs

diff --git a/Documentation/ABI/testing/sysfs-fs-tmpfs b/Documentation/ABI/testing/sysfs-fs-tmpfs
new file mode 100644
index 000000000000..d32b90949710
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-fs-tmpfs
@@ -0,0 +1,13 @@
+What:		/sys/fs/tmpfs/<disk>/acct_errors
+Date:		March 2022
+Contact:	"Gabriel Krisman Bertazi" <krisman@collabora.com>
+Description:
+		Track the number of IO errors caused by lack of memory to
+		perform the allocation of a tmpfs block.
+
+What:		/sys/fs/tmpfs/<disk>/space_errors
+Date:		March 2022
+Contact:	"Gabriel Krisman Bertazi" <krisman@collabora.com>
+Description:
+		Track the number of IO errors caused by lack of space
+		in the filesystem to perform the allocation of a tmpfs block.
diff --git a/mm/shmem.c b/mm/shmem.c
index 8fe4a22e83a6..5c665b955ceb 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -214,6 +214,7 @@ static inline bool shmem_inode_acct_block(struct inode *inode, long pages)
 
 	if (shmem_acct_block(info->flags, pages)) {
 		sbinfo->acct_errors += 1;
+		sysfs_notify(&sbinfo->kobj, NULL, "acct_errors");
 		return false;
 	}
 
@@ -228,6 +229,7 @@ static inline bool shmem_inode_acct_block(struct inode *inode, long pages)
 
 unacct:
 	sbinfo->space_errors += 1;
+	sysfs_notify(&sbinfo->kobj, NULL, "space_errors");
 	shmem_unacct_blocks(info->flags, pages);
 	return false;
 }
@@ -3584,10 +3586,33 @@ static int shmem_show_options(struct seq_file *seq, struct dentry *root)
 }
 
 #if defined(CONFIG_SYSFS)
+static ssize_t acct_errors_show(struct kobject *kobj,
+				struct kobj_attribute *attr, char *page)
+{
+	struct shmem_sb_info *sbinfo =
+		container_of(kobj, struct shmem_sb_info, kobj);
+
+	return sysfs_emit(page, "%lu\n", sbinfo->acct_errors);
+}
+
+static ssize_t space_errors_show(struct kobject *kobj,
+				 struct kobj_attribute *attr, char *page)
+{
+	struct shmem_sb_info *sbinfo =
+		container_of(kobj, struct shmem_sb_info, kobj);
+
+	return sysfs_emit(page, "%lu\n", sbinfo->space_errors);
+}
+
 #define TMPFS_SB_ATTR_RO(name)	\
 	static struct kobj_attribute tmpfs_sb_attr_##name = __ATTR_RO(name)
 
+TMPFS_SB_ATTR_RO(acct_errors);
+TMPFS_SB_ATTR_RO(space_errors);
+
 static struct attribute *tmpfs_attrs[] = {
+	&tmpfs_sb_attr_acct_errors.attr,
+	&tmpfs_sb_attr_space_errors.attr,
 	NULL
 };
 ATTRIBUTE_GROUPS(tmpfs);
-- 
2.35.1