Re: [PATCH v5 1/6] mm/zswap: Fix global shrinker when memory cgroup is disabled

[Hao Jia <jiahao.kernel@gmail.com>]

On 2026/7/1 00:02, Yosry Ahmed wrote:
>> How about something like this? If there are no objections, I'll fold
>> this into the next version.
>>
>>       mm/zswap: Fix global shrinker when memory cgroup is disabled
>>
>>       When memory cgroup is disabled, mem_cgroup_iter() always returns NULL.
>>       Therefore, the global shrinker shrink_worker() always takes the !memcg
>>       branch. After MAX_RECLAIM_RETRIES empty walks, the worker simply
>> gives up,
>>       so it fails to write back anything.
>>
>>       Therefore, when memory cgroup is disabled, fall through with the !memcg
>>       branch and shrink the root memcg directly.
>>
>>       With memcg disabled, shrink_memcg() only returns -ENOENT when the root
>>       LRU is empty, which means the total pages are already below thr.
>> The loop
>>       then safely bails out via the zswap_total_pages() <= thr check. For any
>>       other return value from shrink_memcg(), the loop is guaranteed to
>> terminate,
>>       either after MAX_RECLAIM_RETRIES failures or once the threshold is met.
>>
>>       Fixes: a65b0e7607cc ("zswap: make shrinking memcg-aware")
>>       Cc: stable@vger.kernel.org
>>       Reported-by: Yosry Ahmed <yosry@kernel.org>
>>       Closes:
>> https://lore.kernel.org/all/CAO9r8zPVzMKFbCixxD-qgtRrkFxWVrHiZZeLc=eyTPKPVQgX4g@mail.gmail.com
>>       Signed-off-by: Hao Jia <jiahao1@lixiang.com>
> 
> Feel free to add:
> 
> Acked-by: Yosry Ahmed <yosry@kernel.org>

Thank you for taking the time to review this.
> 
> A small nit below.
> 
>>
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index 4b5149173b0e..9d4f19fc440e 100644
>> --- a/mm/zswap.c
>> +++ b/mm/zswap.c
>> @@ -1361,11 +1361,12 @@ static void shrink_worker(struct work_struct *w)
>>                   } while (memcg && !mem_cgroup_tryget_online(memcg));
>>                   spin_unlock(&zswap_shrink_lock);
>>
>> -               if (!memcg) {
>> -                       /*
>> -                        * Continue shrinking without incrementing
>> failures if
>> -                        * we found candidate memcgs in the last tree walk.
>> -                        */
>> +               /*
>> +                * A NULL memcg ends a full hierarchy pass (except when
>> memcg is
>> +                * disabled, where it is always NULL: fall through to
>> the root LRU).
>> +                * Count a failure only if the pass found no candidates.
> 
> I think "last pass" is clearer than just "pass" here?


Will do.

Thanks,
Hao