From 64748b1645b81399d01ad86657c5bbe097c1701c Mon Sep 17 00:00:00 2001
From: Joe Thornber <ejt@redhat.com>
Date: Wed, 8 Nov 2017 06:41:43 -0500
Subject: [PATCH] dm cache background tracker: limit amount of background work
 that may be issued at once
Git-commit: 64748b1645b81399d01ad86657c5bbe097c1701c
Patch-mainline: v4.15-rc1
References: bsc#1093023

On large systems the cache policy can be over enthusiastic and queue far
too much dirty data to be written back.  This consumes memory.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Coly Li <colyli@suse.de>

---
 drivers/md/dm-cache-background-tracker.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/md/dm-cache-background-tracker.c b/drivers/md/dm-cache-background-tracker.c
index 707233891291..1d0af0a21fc7 100644
--- a/drivers/md/dm-cache-background-tracker.c
+++ b/drivers/md/dm-cache-background-tracker.c
@@ -161,8 +161,17 @@ EXPORT_SYMBOL_GPL(btracker_nr_demotions_queued);
 
 static bool max_work_reached(struct background_tracker *b)
 {
-	// FIXME: finish
-	return false;
+	return atomic_read(&b->pending_promotes) +
+		atomic_read(&b->pending_writebacks) +
+		atomic_read(&b->pending_demotes) >= b->max_work;
+}
+
+struct bt_work *alloc_work(struct background_tracker *b)
+{
+	if (max_work_reached(b))
+		return NULL;
+
+	return kmem_cache_alloc(b->work_cache, GFP_NOWAIT);
 }
 
 int btracker_queue(struct background_tracker *b,
@@ -174,10 +183,7 @@ int btracker_queue(struct background_tracker *b,
 	if (pwork)
 		*pwork = NULL;
 
-	if (max_work_reached(b))
-		return -ENOMEM;
-
-	w = kmem_cache_alloc(b->work_cache, GFP_NOWAIT);
+	w = alloc_work(b);
 	if (!w)
 		return -ENOMEM;
 
-- 
2.16.3