The new shrinker infrastructure in mmotm looks like it will make this
problem worse.
old code:
shrink_slab()
for_each_shrinker {
do_shrinker_shrink(); // one per batch
prune_super()
grab_super_passive()
}
}
Which means we've got at _most_ one grab_super_passive() per batch. The
new code is something like this:
shrink_slab()
{
list_for_each_entry(shrinker, &shrinker_list, list) {
for_each_node_mask(... shrinkctl->nodes_to_scan) {
shrink_slab_node()
}
}
}
shrink_slab_node()
{
max_pass = shrinker->count_objects(shrinker, shrinkctl);
// ^^ does grab_super_passive()
...
while (total_scan >= batch_size) {
ret = shrinker->scan_objects(shrinker, shrinkctl);
// ^^ does grab_super_passive()
}
}
We've got an extra grab_super_passive()s in the case where we are
actually doing a scan, plus we've got the extra for_each_node_mask()
loop. That means even more lock acquisitions in the multi-node NUMA
case, which is exactly where we want to get rid of global lock acquisitions.
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