Re: [PATCH] writeback, cgroup: switch inodes with dirty timestamps to release dying cgwbs

[Jingbo Xu <jefflexu@linux.alibaba.com>]

On 10/13/23 1:31 AM, Tejun Heo wrote:
> On Wed, Oct 11, 2023 at 04:42:28PM +0800, Jingbo Xu wrote:
>> The cgwb cleanup routine will try to release the dying cgwb by switching
>> the attached inodes.  It fetches the attached inodes from wb->b_attached
>> list, omitting the fact that inodes only with dirty timestamps reside in
>> wb->b_dirty_time list, which is the case when lazytime is enabled.  This
>> causes enormous zombie memory cgroup when lazytime is enabled, as inodes
>> with dirty timestamps can not be switched to a live cgwb for a long time.
>>
>> It is reasonable not to switch cgwb for inodes with dirty data, as
>> otherwise it may break the bandwidth restrictions.  However since the
>> writeback of inode metadata is not accounted, let's also switch inodes
>> with dirty timestamps to avoid zombie memory and block cgroups when
>> laztytime is enabled.
>>
>> Fixs: c22d70a162d3 ("writeback, cgroup: release dying cgwbs by switching attached inodes")
>> Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> 
> The patch looks fine to me.
> 
> ...
>> +	restart = isw_prepare_wbs_switch(isw, &wb->b_attached, &nr);
>> +	if (!restart)
>> +		restart = isw_prepare_wbs_switch(isw, &wb->b_dirty_time, &nr);
> 
> But can you add a comment explaining why we're also migrating b_dirty_time?

Will add the comment in the next version.  Thanks.


-- 
Thanks,
Jingbo