On Tue, Aug 13, 2024 at 08:47:14PM GMT, Kinsey Ho <kinseyho@xxxxxxxxxx> wrote:
> @@ -1072,21 +1073,26 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
> * and kicking, and don't take an extra reference.
> */
> if (css == &root->css || css_tryget(css)) {
> - memcg = mem_cgroup_from_css(css);
> break;
> }
> }
>
> + memcg = mem_cgroup_from_css(css);
> +
> if (reclaim) {
> /*
> * The position could have already been updated by a competing
> * thread, so check that the value hasn't changed since we read
> * it to avoid reclaiming from the same cgroup twice.
> */
> - (void)cmpxchg(&iter->position, pos, memcg);
> + if (cmpxchg(&iter->position, pos, memcg) != pos) {
> + if (css && css != &root->css)
> + css_put(css);
> + goto restart;
> + }
I may be missing (literal) context but I'd suggest not moving the memcg
assignment and leverage
if (memcg != NULL)
css_put(memcg->css)
so that the is-root comparison needn't be repeated.
Thanks,
Michal
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