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SubjectRe: [RFC 5/5] Memory controller soft limit reclaim on contention
KOSAKI Motohiro wrote:
> Hi
>
> this code survive stress testing?
>
>
>> + while (count-- &&
>> + ((mem = heap_delete_max(&mem_cgroup_heap)) != NULL)) {
>> + BUG_ON(!mem->on_heap);
>> + spin_unlock_irqrestore(&mem_cgroup_heap_lock, flags);
>> + nr_reclaimed += try_to_free_mem_cgroup_pages(mem,
>> + gfp_mask);
>> + cond_resched();
>> + spin_lock_irqsave(&mem_cgroup_heap_lock, flags);
>> + mem->on_heap = 0;
>> + /*
>> + * What should be the basis of breaking out?
>> + */
>> + if (nr_reclaimed)
>> + goto done;
>
> doubtful shortcut.
> we shouldn't assume we need only one page.
>

There's a comment on top -- what should be the basis of breaking out? It
definitely needs refinement, the current solution seemed to be working, so I
kept it.

>
>
>> #endif /* _LINUX_MEMCONTROL_H */
>> diff -puN mm/vmscan.c~memory-controller-soft-limit-reclaim-on-contention mm/vmscan.c
>> diff -puN mm/page_alloc.c~memory-controller-soft-limit-reclaim-on-contention mm/page_alloc.c
>> --- linux-2.6.26-rc5/mm/page_alloc.c~memory-controller-soft-limit-reclaim-on-contention 2008-06-27 20:43:10.000000000 +0530
>> +++ linux-2.6.26-rc5-balbir/mm/page_alloc.c 2008-06-27 20:43:10.000000000 +0530
>> @@ -1669,7 +1669,14 @@ nofail_alloc:
>> reclaim_state.reclaimed_slab = 0;
>> p->reclaim_state = &reclaim_state;
>>
>> - did_some_progress = try_to_free_pages(zonelist, order, gfp_mask);
>> + /*
>> + * First try to reclaim from memory control groups that have
>> + * exceeded their soft limit
>> + */
>> + did_some_progress = mem_cgroup_reclaim_on_contention(gfp_mask);
>> + if (!did_some_progress)
>> + did_some_progress = try_to_free_pages(zonelist, order,
>> + gfp_mask);
>
> try_to_free_mem_cgroup_pages() assume memcg need only one page.
> but this code break it.
>
> if anyone need several continuous memory, mem_cgroup_reclaim_on_contention() reclaim
> one or a very few page and return >0, then cause page allocation failure.
>
> shouldn't we extend try_to_free_mem_cgroup_pages() agruments?
>
>
> in addition, if we don't assume try_to_free_mem_cgroup_pages() need one page,
> we should implement lumpy reclaim to mem_cgroup_isolate_pages().
> otherwise, cpu wasting significant increase.

The memory controller currently controls just *user* pages, which are all of
order 1. Since pages are faulted in at different times, lumpy reclaim was not
the highest priority for the memory controller. NOTE: the pages are duplicated
on the per-zone LRU, so lumpy reclaim from there should work just fine.

--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL


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