Event merges are expensive when event queue size is large.
Limit the linear search to 128 merge tests.
In combination with 128 hash lists, there is a potential to
merge with up to 16K events in the hashed queue.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/notify/fanotify/fanotify.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 12df6957e4d8..6d3807012851 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -129,11 +129,15 @@ static bool fanotify_should_merge(struct fsnotify_event *old_fsn,
return false;
}
+/* Limit event merges to limit CPU overhead per event */
+#define FANOTIFY_MAX_MERGE_EVENTS 128
+
/* and the list better be locked by something too! */
static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
{
struct fsnotify_event *test_event;
struct fanotify_event *new;
+ int i = 0;
pr_debug("%s: list=%p event=%p\n", __func__, list, event);
new = FANOTIFY_E(event);
@@ -147,6 +151,8 @@ static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
return 0;
list_for_each_entry_reverse(test_event, list, list) {
+ if (++i > FANOTIFY_MAX_MERGE_EVENTS)
+ break;
if (fanotify_should_merge(test_event, event)) {
FANOTIFY_E(test_event)->mask |= new->mask;
return 1;
--
2.25.1
