On Tue, 15 Jun 2010 15:16:01 +0100
Mel Gorman <mel@xxxxxxxxx> wrote:
> On Tue, Jun 15, 2010 at 10:04:24AM -0400, Rik van Riel wrote:
> > On 06/15/2010 09:59 AM, Mel Gorman wrote:
> >> On Tue, Jun 15, 2010 at 09:34:18AM -0400, Rik van Riel wrote:
> >>> On 06/15/2010 07:45 AM, Mel Gorman wrote:
> >
> >>>>>>
> >>>>>> +/* kswapd and memcg can writeback as they are unlikely to overflow stack */
> >>>>>> +static inline bool reclaim_can_writeback(struct scan_control *sc)
> >>>>>> +{
> >>>>>> + return current_is_kswapd() || sc->mem_cgroup != NULL;
> >>>>>> +}
> >
> >>> If direct reclaim can overflow the stack, so can direct
> >>> memcg reclaim. That means this patch does not solve the
> >>> stack overflow, while admitting that we do need the
> >>> ability to get specific pages flushed to disk from the
> >>> pageout code.
> >>>
> >>
> >> What path is taken with memcg != NULL that could overflow the stack? I
> >> couldn't spot one but mm/memcontrol.c is a bit tangled so finding all
> >> its use cases is tricky. The critical path I had in mind though was
> >> direct reclaim and for that path, memcg == NULL or did I miss something?
> >
> > mem_cgroup_hierarchical_reclaim -> try_to_free_mem_cgroup_pages
> >
>
> But in turn, where is mem_cgroup_hierarchical_reclaim called from direct
> reclaim? It appears to be only called from the fault path or as a result
> of the memcg changing size.
>
yes. It's only called from
- page fault
- add_to_page_cache()
I think we'll see no stack problem. Now, memcg doesn't wakeup kswapd for
reclaiming memory, it needs direct writeback.
Thanks,
-Kame
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