Re: memory cgroup pagecache and inode problem

[Yang Shi <shy828301@gmail.com>]

On Tue, Jan 15, 2019 at 11:06 PM Michal Hocko <mhocko@kernel.org> wrote:
>
> On Wed 16-01-19 11:52:08, Fam Zheng wrote:
> [...]
> > > This is what force_empty is supposed to do.  But, as your test shows
> > > some page cache may still remain after force_empty, then cause offline
> > > memcgs accumulated.  I haven't figured out what happened.  You may try
> > > what Michal suggested.
> >
> > None of the existing patches helped so far, but we suspect that the
> > pages cannot be locked at the force_empty moment. We have being
> > working on a “retry” patch which does solve the problem. We’ll
> > do more tracing (to have a better understanding of the issue) and post
> > the findings and/or the patch later. Thanks.
>
> Just for the record. There was a patch to remove
> MEM_CGROUP_RECLAIM_RETRIES restriction in the path. I cannot find the
> link right now but that is something we certainly can do. The context is
> interruptible by signal and it from my experience any retry count can

Do you mean this one https://lore.kernel.org/patchwork/patch/865835/ ?

I think removing retries is feasible as long as exit is handled correctly.

Yang

> lead to unexpected failures. But I guess you really want to check
> vmscan tracepoints to see why you cannot reclaim pages on memcg LRUs
> first.
> --
> Michal Hocko
> SUSE Labs