[RFC PATCH v4 01/20] mm: add bdi_set_strict_limit() function

[Stefan Roesch <shr@devkernel.io>]

This adds the bdi_set_strict_limit function to be able to set/unset the
BDI_CAP_STRICTLIMIT flag.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
 include/linux/backing-dev.h |  1 +
 mm/page-writeback.c         | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 439815cc1ab9..9c984ffc8a0a 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -104,6 +104,7 @@ static inline unsigned long wb_stat_error(void)
 
 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio);
 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
+int bdi_set_strict_limit(struct backing_dev_info *bdi, unsigned int strict_limit);
 
 /*
  * Flags in backing_dev_info::capability
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 7e9d8d857ecc..3745b886722f 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -698,6 +698,21 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
 }
 EXPORT_SYMBOL(bdi_set_max_ratio);
 
+int bdi_set_strict_limit(struct backing_dev_info *bdi, unsigned int strict_limit)
+{
+	if (strict_limit > 1)
+		return -EINVAL;
+
+	spin_lock_bh(&bdi_lock);
+	if (strict_limit)
+		bdi->capabilities |= BDI_CAP_STRICTLIMIT;
+	else
+		bdi->capabilities &= ~BDI_CAP_STRICTLIMIT;
+	spin_unlock_bh(&bdi_lock);
+
+	return 0;
+}
+
 static unsigned long dirty_freerun_ceiling(unsigned long thresh,
 					   unsigned long bg_thresh)
 {
-- 
2.30.2