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fanotify: limit number of event merge attempts

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Event merges are expensive when event queue size is large, so limit the
linear search to 128 merge tests.

In combination with 128 size hash table, there is a potential to merge
with up to 16K events in the hashed queue.

Link: https://lore.kernel.org/r/20210304104826.3993892-6-amir73il@gmail.com
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Amir Goldstein 2021-03-04 12:48:26 +02:00 committed by Jan Kara
parent 94e00d28a6
commit b8cd0ee8cd
1 changed files with 6 additions and 0 deletions
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6
fs/notify/fanotify/fanotify.c
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@ -148,6 +148,9 @@ static bool fanotify_should_merge(struct fanotify_event *old,
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 fsnotify_group *group,
struct fsnotify_event *event)
@ -155,6 +158,7 @@ static int fanotify_merge(struct fsnotify_group *group,
struct fanotify_event *old, *new = FANOTIFY_E(event);
unsigned int bucket = fanotify_event_hash_bucket(group, new);
struct hlist_head *hlist = &group->fanotify_data.merge_hash[bucket];
int i = 0;
pr_debug("%s: group=%p event=%p bucket=%u\n", __func__,
group, event, bucket);
@ -168,6 +172,8 @@ static int fanotify_merge(struct fsnotify_group *group,
return 0;
hlist_for_each_entry(old, hlist, merge_list) {
if (++i > FANOTIFY_MAX_MERGE_EVENTS)
break;
if (fanotify_should_merge(old, new)) {
old->mask |= new->mask;
return 1;