On Mon 26-11-12 15:19:18, Johannes Weiner wrote:

On Mon, Nov 26, 2012 at 09:08:48PM +0100, Michal Hocko wrote:

[...]

quoted

OK, I guess I am getting what you are trying to say. So what you are
suggesting is to just let mem_cgroup_out_of_memory send the signal and
move on without retry (or with few charge retries without further OOM
killing) and fail the charge with your new FAULT_OOM_HANDLED (resp.
something like FAULT_RETRY) error code resp. ENOMEM depending on the
caller.  OOM disabled case would be "you are on your own" because this
has been dangerous anyway. Correct?

Yes.

quoted

I do agree that the current endless retry loop is far from being ideal
and can see some updates but I am quite nervous about any potential
regressions in this area (e.g. too aggressive OOM etc...). I have to
think about it some more.

Agreed on all points.  Maybe we can keep a couple of the oom retry
iterations or something like that, which is still much more than what
global does and I don't think the global OOM killer is overly eager.

Yes we can offer less blood and more confort

Testing will show more.

quoted

Anyway if you have some more specific ideas I would be happy to review
patches.

Okay, I just wanted to check back with you before going down this
path.  What are we going to do short term, though?  Do you want to
push the disable-oom-for-pagecache for now or should we put the
VM_FAULT_OOM_HANDLED fix in the next version and do stable backports?

This issue has been around for a while so frankly I don't think it's
urgent enough to rush things.

Yes, but now we have a real usecase where this hurts AFAIU. Unless
we come up with a fix/reasonable workaround I would rather go with
something simpler for starter and more sofisticated later.

I have to double check other places where we do charging but the last
time I've checked we don't hold page locks on already visible pages (we
do precharge in __do_fault f.e.), mem_map for reading in the page fault
path is also safe (with oom enabled) and I guess that tmpfs is ok as
well. Then we have a page cache and that one should be covered by my
patch. So we should be covered.

But I like your idea long term.

Thanks!
-- 
Michal Hocko
SUSE Labs