Re: [RFC PATCH] memcg, oom: move out_of_memory back to the charge path

[Johannes Weiner]

On Wed, Jun 20, 2018 at 05:31:48PM +0200, Michal Hocko wrote:
> This?
> 	if (order > PAGE_ALLOC_COSTLY_ORDER)
> 		return OOM_SKIPPED;
> 
> 	/*
> 	 * We are in the middle of the charge context here, so we
> 	 * don't want to block when potentially sitting on a callstack
> 	 * that holds all kinds of filesystem and mm locks.
> 	 *
> 	 * cgroup1 allows disabling the OOM killer and waiting for outside
> 	 * handling until the charge can succeed; remember the context and put
> 	 * the task to sleep at the end of the page fault when all locks are
> 	 * released.
> 	 *
> 	 * On the other hand, in-kernel OOM killer allows for an async victim
> 	 * memory reclaim (oom_reaper) and that means that we are not solely
> 	 * relying on the oom victim to make a forward progress and we can
> 	 * invoke the oom killer here.
> 	 *
> 	 * Please note that mem_cgroup_oom_synchronize might fail to find a
> 	 * victim and then we have rely on mem_cgroup_oom_synchronize otherwise
> 	 * we would fall back to the global oom killer in pagefault_out_of_memory
> 	 */
> 	if (memcg->oom_kill_disable) {
> 		if (!current->memcg_may_oom)
> 			return OOM_SKIPPED;
> 		css_get(&memcg->css);
> 		current->memcg_in_oom = memcg;
> 		current->memcg_oom_gfp_mask = mask;
> 		current->memcg_oom_order = order;
> 
> 		return OOM_ASYNC;
> 	}
> 
> 	if (mem_cgroup_out_of_memory(memcg, mask, order))
> 		return OOM_SUCCESS;
> 
> 	WARN(!current->memcg_may_oom,
> 			"Memory cgroup charge failed because of no reclaimable memory! "
> 			"This looks like a misconfiguration or a kernel bug.");
> 	return OOM_FAILED;

Yep, this looks good IMO.