| Message ID | 20210915182008.1369659-1-amir73il@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [5.10] fanotify: limit number of event merge attempts | expand |
On Wed, Sep 15, 2021 at 09:20:08PM +0300, Amir Goldstein wrote: > commit b8cd0ee8cda68a888a317991c1e918a8cba1a568 upstream. > > Event merges are expensive when event queue size is large, so limit the > linear search to 128 merge tests. > > [Stable backport notes] The following statement from upstream commit is > irrelevant for backport: > - > -In combination with 128 size hash table, there is a potential to merge > -with up to 16K events in the hashed queue. > - > [Stable backport notes] The problem is as old as fanotify and described > in the linked cover letter "Performance improvement for fanotify merge". > This backported patch fixes the performance issue at the cost of merging > fewer potential events. Fixing the performance issue is more important > than preserving the "event merge" behavior, which was not predictable in > any way that applications could rely on. > > 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> > Cc: <stable@vger.kernel.org> > Link: https://lore.kernel.org/linux-fsdevel/20210202162010.305971-1-amir73il@gmail.com/ > Link: https://lore.kernel.org/linux-fsdevel/20210915163334.GD6166@quack2.suse.cz/ > Signed-off-by: Amir Goldstein <amir73il@gmail.com> > --- > fs/notify/fanotify/fanotify.c | 6 ++++++ > 1 file changed, 6 insertions(+) Now queued up, thanks. greg k-h
diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c index 1192c9953620..c3af99e94f1d 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;