Hello,

On Fri, Aug 16, 2019 at 06:02:56PM +0200, Jan Kara wrote:

1) You ask to writeback LONG_MAX pages. That means that you give up any
livelock avoidance for the flusher work and you can writeback almost
forever if someone is busily dirtying pages in the wb. I think you need to
pick something like amount of dirty pages in the given wb (that would have
to be fetched after everything is looked up) or just some arbitrary
reasonably small constant like 1024 (but then I guess there's no guarantee
stuck memcg will make any progress and you've invalidated the frn entry
here).

I see.  Yeah, I think the right thing to do would be feeding the
number of dirty pages or limiting it to one full sweep.  I'll look
into it.

2) When you invalidate frn entry here by writing 0 to 'at', it's likely to get
reused soon. Possibly while the writeback is still running. And then you
won't start any writeback for the new entry because of the
atomic_read(&frn->done.cnt) == 1 check. This seems like it could happen
pretty frequently?

Hmm... yeah, the clearing might not make sense.  I'll remove that.

Thanks.

-- 
tejun