Pavel Emelyanov wrote:
> The /sys/slab/<name>/cache_notify attribute controls
> whether the cache <name> is to be accounted or not.
>
> By default no caches are accountable. Simply make
> # echo -n 1 > /sys/slab/<name>cache_notify
> to turn notification of this cache on.
>
> If we turn accounting on on some cache and this cache
> is merged with some other, this "other" will be notified
> as well. One can solve this by disabling of cache merging,
> i.e. booting with slub_nomerge option to the kernel.
>
> Turning the notifications "on" causes all te subsequent
> allocations use the slow allocation path, so all the
> per-cpu caches are flushed and all the partial pages
> are marked as SlabDebug.
>
Do we know of the overhead of slub notifications? It would
be nice to know and probably add it to the help text in
Kconfig.
> ---
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 31d04a3..e066a0e 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3779,6 +3932,60 @@ static ssize_t defrag_ratio_store(struct
> SLAB_ATTR(defrag_ratio);
> #endif
>
> +static ssize_t cache_notify_show(struct kmem_cache *s, char *buf)
> +{
> + return sprintf(buf, "%d\n", !!(s->flags & SLAB_NOTIFY));
> +}
> +
> +static ssize_t cache_notify_store(struct kmem_cache *s,
> + const char *buf, size_t length)
> +{
> + int err;
> + int n;
> +
> + if ((buf[0] == '1') && !(s->flags & SLAB_NOTIFY)) {
Won't this code break if I pass 10 as input in buf?
> + err = slub_on_notify(s);
> + if (err < 0)
> + return err;
> +
> + s->flags |= SLAB_NOTIFY;
> +
> + flush_all(s);
Sounds like an expensive operation, can we add a comment
to indicate the same. Also, in the documentation, could
we warn the user that turning notifications on/off
can be expensive?
> + for_each_node_state(n, N_NORMAL_MEMORY) {
> + struct kmem_cache_node *node;
> + struct page *pg;
> +
> + node = get_node(s, n);
> + spin_lock_irq(&node->list_lock);
> + list_for_each_entry(pg, &node->partial, lru)
> + SetSlabDebug(pg);
> + spin_unlock_irq(&node->list_lock);
> + }
> + return length;
> + }
> +
> + if ((buf[0] == '0') && (s->flags & SLAB_NOTIFY)) {
What happens if buf is 01?
> + /*
> + * TODO: make the notifications-off work
> + */
> + if (any_slab_objects(s))
> + return -EBUSY;
> +
> + s->flags &= ~SLAB_NOTIFY;
> + err = slub_off_notify(s);
> + if (err < 0) {
> + s->flags |= SLAB_NOTIFY;
> + return err;
> + }
> +
> + return length;
> + }
> +
> + return -EINVAL;
> +}
> +
> +SLAB_ATTR(cache_notify);
> +
> static struct attribute * slab_attrs[] = {
> &slab_size_attr.attr,
> &object_size_attr.attr,
> @@ -3809,6 +4016,7 @@ static struct attribute * slab_attrs[] =
> #ifdef CONFIG_NUMA
> &defrag_ratio_attr.attr,
> #endif
> + &cache_notify_attr.attr,
> NULL
> };
>
>
--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL
_______________________________________________
Devel mailing list
[email protected]
https://openvz.org/mailman/listinfo/devel
