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SubjectRe: [RFC] sysfs: defer instantiation of default attrs
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Hi Ed:

Thank for taking the to look into this.

On 2/20/16 3:42 AM, Edward Cree wrote:
> Testing this in a VM, and with udevd disabled (being too lazy to do it
> properly), created 1024 bridges. On ls'ing
> /sys/class/net/bridge*/queues/*/, saw free memory drop by 64kB,
> suggesting that much had been saved by deferral. It's not very much,
> hopefully deferring attribute groups will do better.

That sounds consistent with what I found by cutting out attributes in
netdev_register_kobject. e.g., from my patch:

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index b6c8a6629b39..f0df828a2f20 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1524,7 +1524,8 @@ int netdev_register_kobject(struct net_device *ndev)
int error = 0;

device_initialize(dev);
- dev->class = &net_class;
+ if (!netif_is_lwt(ndev))
+ dev->class = &net_class;
dev->platform_data = ndev;
dev->groups = groups;

@@ -1535,7 +1536,8 @@ int netdev_register_kobject(struct net_device *ndev)
if (*groups)
groups++;

- *groups++ = &netstat_group;
+ if (!netif_is_lwt(ndev)) {
+ *groups++ = &netstat_group;

#if IS_ENABLED(CONFIG_WIRELESS_EXT) || IS_ENABLED(CONFIG_CFG80211)
if (ndev->ieee80211_ptr)

The big memory savings came in when I bypassed register_queue_kobjects:

error = device_add(dev);
if (error)
return error;
- error = register_queue_kobjects(ndev);
- if (error) {
- device_del(dev);
- return error;
+ if (!netif_is_lwt(ndev)) {
+ error = register_queue_kobjects(ndev);
+ if (error) {
+ device_del(dev);
+ return error;
+ }
}
pm_runtime_set_memalloc_noio(dev, true);


Yes, this is a bit Draconian and does have impacts to tools looking for
/sys files but the return is huge when you look at 1000's of netdevices
(ports, vlans, bridges, bonds).


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