Re: [PATCH] mm, vmscan: guarantee drop_slab_node() termination

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2021/8/19 5:48, Chris Down wrote:
> Vlastimil Babka writes:
>> @@ -948,7 +949,7 @@ void drop_slab_node(int nid)
>>         do {
>>             freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
>>         } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
>> -    } while (freed > 10);
>> +    } while ((freed >> shift++) > 0);
>
> I think this is a good idea, thanks for bringing it up :-)
>
> I'm not sure about the bitshift idea, though. It certainly makes sure 
> that even large, continuous periods of reclaim eventually terminates, 
> but I find it hard to reason about -- for example, if there's a lot of 
> parallel activity, that might result in 10 constantly reintroduced 
> pages, or 1000 pages, and it's not immediately obvious that we should 
> treat those differently.
>
> What about using MAX_RECLAIM_RETRIES? There's already precedent for 
> using it in non-OOM scenarios, like mem_cgroup_handle_over_high.

Yes, we meet this issue too, and we add a max loop limit in 
drop_slab_node() in our kernel, which also could be reconfigured by 
sysctl ;)

>
> .
>