2011/6/23 Michal Hocko [off-list ref]:

On Thu 23-06-11 19:01:57, KAMEZAWA Hiroyuki wrote:

quoted

On Thu, 23 Jun 2011 11:02:04 +0200
Michal Hocko [off-list ref] wrote:

quoted

On Thu 23-06-11 17:08:11, KAMEZAWA Hiroyuki wrote:

quoted

On Thu, 23 Jun 2011 09:41:33 +0200
Michal Hocko [off-list ref] wrote:

[...]

quoted

quoted

Other than that:
Reviewed-by: Michal Hocko <redacted>

I found the page is added to LRU before charging. (In this case,
memcg's LRU is ignored.) I'll post a new version with a fix.

Yes, you are right. I have missed that.
This means that we might race with reclaim which could evict the COWed
page wich in turn would uncharge that page even though we haven't
charged it yet.

Can we postpone page_add_new_anon_rmap to the charging path or it would
just race somewhere else?

I got a different idea. How about this ?
I think this will have benefit for non-memcg users under OOM, too.

Could you be more specific? I do not see how preallocation which might
turn out to be pointless could help under OOM.

We'll have no page allocation under lock_page() held in this path.
I think it is good.

quoted

A concerns is VM_FAULT_RETRY case but wait-for-lock will be much heavier
than preallocation + free-for-retry cost.

Preallocation is rather costly when fault handler fails (e.g. SIGBUS
which is the easiest one to trigger).

I think pcp cache of free page allocater does enough good job and I guess
we'll see no problem even if there is a storm of SIGBUS.

I am not saying this approach is bad but I think that preallocation can
be much more costly than unlock, charge and lock&recheck approach.

memcg_is_disabled() cannot help ROOT cgroup. And additional
lock/unlock method may kill FAULT_RETRY at lock contention optimization
which was added recently.


Thanks,
-Kame

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