On Tue 02-02-21 18:20:06, Amir Goldstein wrote:
> On 64bit arch, use the available 32bit in event for next_bucket field,
> that is used to chain all events by order of insertion.
>
> The group has a cursor for the bucket containing the first event and
> every event stores the bucket of the next event to read.
>
> On 32bit arch, hashed notification queue is disabled.
I would not bother with saving 4-bytes per event on 32-bit archs... IMHO it
is just not worth the additional code complexity and ifdefs...
Otherwise the patch looks fine.
Honza
>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> fs/notify/notification.c | 49 ++++++++++++++++++++++++--------
> include/linux/fsnotify_backend.h | 42 +++++++++++++++++++++++++++
> 2 files changed, 79 insertions(+), 12 deletions(-)
>
> diff --git a/fs/notify/notification.c b/fs/notify/notification.c
> index 58c8f6c1be1b..d98f4c8bfb0e 100644
> --- a/fs/notify/notification.c
> +++ b/fs/notify/notification.c
> @@ -84,8 +84,8 @@ static void fsnotify_queue_check(struct fsnotify_group *group)
> if (fsnotify_notify_queue_is_empty(group))
> return;
>
> - first_empty = list_empty(&group->notification_list[group->first_bucket]);
> - last_empty = list_empty(&group->notification_list[group->last_bucket]);
> + first_empty = WARN_ON_ONCE(list_empty(&group->notification_list[group->first_bucket]));
> + last_empty = WARN_ON_ONCE(list_empty(&group->notification_list[group->last_bucket]));
>
> list = &group->notification_list[0];
> for (i = 0; i <= group->max_bucket; i++, list++) {
> @@ -121,12 +121,23 @@ static void fsnotify_queue_event(struct fsnotify_group *group,
>
> pr_debug("%s: group=%p event=%p bucket=%u\n", __func__, group, event, b);
>
> - /*
> - * TODO: set next_bucket of last event.
> - */
> - group->last_bucket = b;
> - if (!group->num_events)
> - group->first_bucket = b;
> + if (fsnotify_notify_queue_is_hashed(group)) {
> + /*
> + * On first insert, set this event's list as the list to read first event.
> + * Otherwise, point from last event to this event's list.
> + */
> + struct list_head *last_l = &group->notification_list[group->last_bucket];
> +
> + if (!group->num_events) {
> + group->first_bucket = b;
> + } else if (!WARN_ON_ONCE(list_empty(last_l))) {
> + struct fsnotify_event *last_e;
> +
> + last_e = list_last_entry(last_l, struct fsnotify_event, list);
> + fsnotify_event_set_next_bucket(last_e, b);
> + }
> + group->last_bucket = b;
> + }
> group->num_events++;
> list_add_tail(&event->list, list);
> }
> @@ -186,8 +197,8 @@ int fsnotify_add_event(struct fsnotify_group *group,
> return ret;
> }
>
> -void fsnotify_remove_queued_event(struct fsnotify_group *group,
> - struct fsnotify_event *event)
> +static void __fsnotify_remove_queued_event(struct fsnotify_group *group,
> + struct fsnotify_event *event)
> {
> assert_spin_locked(&group->notification_lock);
> /*
> @@ -198,6 +209,17 @@ void fsnotify_remove_queued_event(struct fsnotify_group *group,
> group->num_events--;
> }
>
> +void fsnotify_remove_queued_event(struct fsnotify_group *group,
> + struct fsnotify_event *event)
> +{
> + /*
> + * if called for removal of event in the middle of a hashed queue,
> + * events may be read not in insertion order.
> + */
> + WARN_ON_ONCE(fsnotify_notify_queue_is_hashed(group));
> + __fsnotify_remove_queued_event(group, event);
> +}
> +
> /* Return the notification list of the first event */
> struct list_head *fsnotify_first_notification_list(struct fsnotify_group *group)
> {
> @@ -213,6 +235,7 @@ struct list_head *fsnotify_first_notification_list(struct fsnotify_group *group)
> return list;
>
> /*
> + * Oops... first bucket is not supposed to be empty.
> * Look for any non-empty bucket.
> */
> fsnotify_queue_check(group);
> @@ -239,10 +262,12 @@ struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
> pr_debug("%s: group=%p bucket=%u\n", __func__, group, group->first_bucket);
>
> event = list_first_entry(list, struct fsnotify_event, list);
> - fsnotify_remove_queued_event(group, event);
> + __fsnotify_remove_queued_event(group, event);
> /*
> - * TODO: update group->first_bucket to next_bucket in first event.
> + * Removed event points to the next list to read from.
> */
> + group->first_bucket = fsnotify_event_next_bucket(event);
> +
> return event;
> }
>
> diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
> index b2a80bc00108..3fc3c9e4d21c 100644
> --- a/include/linux/fsnotify_backend.h
> +++ b/include/linux/fsnotify_backend.h
> @@ -161,9 +161,12 @@ struct fsnotify_ops {
> };
>
> #ifdef CONFIG_FANOTIFY
> +#if BITS_PER_LONG == 64
> +/* Use available 32bit of event for hashed queue support */
> #define FSNOTIFY_HASHED_QUEUE
> #define FSNOTIFY_HASHED_QUEUE_MAX_BITS 8
> #endif
> +#endif
>
> /*
> * all of the information about the original object we want to now send to
> @@ -173,6 +176,9 @@ struct fsnotify_ops {
> struct fsnotify_event {
> struct list_head list;
> unsigned int key; /* Key for hashed queue add/merge */
> +#ifdef FSNOTIFY_HASHED_QUEUE
> + unsigned int next_bucket; /* Bucket to read next event from */
> +#endif
> };
>
> /*
> @@ -277,6 +283,41 @@ static inline struct list_head *fsnotify_event_notification_list(
> return &group->notification_list[fsnotify_event_bucket(group, event)];
> }
>
> +#ifdef FSNOTIFY_HASHED_QUEUE
> +static inline bool fsnotify_notify_queue_is_hashed(struct fsnotify_group *group)
> +{
> + return group->max_bucket > 0;
> +}
> +
> +static inline unsigned int fsnotify_event_next_bucket(struct fsnotify_event *event)
> +{
> + return event->next_bucket;
> +}
> +
> +static inline void fsnotify_event_set_next_bucket(struct fsnotify_event *event,
> + unsigned int b)
> +{
> + event->next_bucket = b;
> +}
> +
> +#else
> +static inline bool fsnotify_notify_queue_is_hashed(struct fsnotify_group *group)
> +{
> + return false;
> +}
> +
> +static inline unsigned int fsnotify_event_next_bucket(struct fsnotify_event *event)
> +{
> + return 0;
> +}
> +
> +static inline void fsnotify_event_set_next_bucket(struct fsnotify_event *event,
> + unsigned int b)
> +{
> +}
> +
> +#endif
> +
> /* When calling fsnotify tell it if the data is a path or inode */
> enum fsnotify_data_type {
> FSNOTIFY_EVENT_NONE,
> @@ -620,6 +661,7 @@ static inline void fsnotify_init_event(struct fsnotify_event *event,
> {
> INIT_LIST_HEAD(&event->list);
> event->key = key;
> + fsnotify_event_set_next_bucket(event, 0);
> }
>
> #else
> --
> 2.25.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
