Re: [patch 0/8] mm: memcg naturalization -rc2

Greg Thelen
2011-06-02T00:36:07Z

On Wed, Jun 1, 2011 at 4:52 PM, Hiroyuki Kamezawa
<kamezawa.hiroyuki@gmail.com> wrote:
> 2011/6/1 Johannes Weiner <hannes@cmpxchg.org>:
>> Hi,
>>
>> this is the second version of the memcg naturalization series.  The
>> notable changes since the first submission are:
>>
>>    o the hierarchy walk is now intermittent and will abort and
>>      remember the last scanned child after sc->nr_to_reclaim pages
>>      have been reclaimed during the walk in one zone (Rik)
>>
>>    o the global lru lists are never scanned when memcg is enabled
>>      after #2 'memcg-aware global reclaim', which makes this patch
>>      self-sufficient and complete without requiring the per-memcg lru
>>      lists to be exclusive (Michal)
>>
>>    o renamed sc->memcg and sc->current_memcg to sc->target_mem_cgroup
>>      and sc->mem_cgroup and fixed their documentation, I hope this is
>>      better understandable now (Rik)
>>
>>    o the reclaim statistic counters have been renamed.  there is no
>>      more distinction between 'pgfree' and 'pgsteal', it is now
>>      'pgreclaim' in both cases; 'kswapd' has been replaced by
>>      'background'
>>
>>    o fixed a nasty crash in the hierarchical soft limit check that
>>      happened during global reclaim in memcgs that are hierarchical
>>      but have no hierarchical parents themselves
>>
>>    o properly implemented the memcg-aware unevictable page rescue
>>      scanner, there were several blatant bugs in there
>>
>>    o documentation on new public interfaces
>>
>> Thanks for your input on the first version.
>>
>> I ran microbenchmarks (sparse file catting, essentially) to stress
>> reclaim and LRU operations.  There is no measurable overhead for
>> !CONFIG_MEMCG, memcg disabled during boot, memcg enabled but no
>> configured groups, and hard limit reclaim.
>>
>> I also ran single-threaded kernbenchs in four unlimited memcgs in
>> parallel, contained in a hard-limited hierarchical parent that put
>> constant pressure on the workload.  There is no measurable difference
>> in runtime, the pgpgin/pgpgout counters, and fairness among memcgs in
>> this test compared to an unpatched kernel.  Needs more evaluation,
>> especially with a higher number of memcgs.
>>
>> The soft limit changes are also proven to work in so far that it is
>> possible to prioritize between children in a hierarchy under pressure
>> and that runtime differences corresponded directly to the soft limit
>> settings in the previously described kernbench setup with staggered
>> soft limits on the groups, but this needs quantification.
>>
>> Based on v2.6.39.
>>
>
> Hmm, I welcome and will review this patches but.....some points I want to say.
>
> 1. No more conflict with Ying's work ?
>    Could you explain what she has and what you don't in this v2 ?
>    If Ying's one has something good to be merged to your set, please
> include it.
>
> 2. it's required to see performance score in commit log.
>
> 3. I think dirty_ratio as 1st big patch to be merged. (But...hmm..Greg ?
>    My patches for asynchronous reclaim is not very important. I can rework it.

I am testing the next version (v8) of the memcg dirty ratio patches. I expect
to have it posted for review later this week.

> 4. This work can be splitted into some small works.
>     a) fix for current code and clean ups
>     a') statistics
>     b) soft limit rework
>     c) change global reclaim
>
>  I like (a)->(b)->(c) order. and while (b) you can merge your work
> with Ying's one.
>  And for a') , I'd like to add a new file memory.reclaim_stat as I've
> already shown.
>  and allow resetting.
>
>  Hmm, how about splitting patch 2/8 into small patches and see what happens in
>  3.2 or 3.3 ? While that, we can make softlimit works better.
>  (and once we do 2/8, our direction will be fixed to the direction to
> remove global LRU.)
>
> 5. please write documentation to explain what new LRU do.
>
> BTW, after this work, lists of ROOT cgroup comes again. I may need to check
> codes which see memcg is ROOT or not. Because we removed many atomic
> ops in memcg, I wonder ROOT cgroup can be accounted again..
>
> Thanks,
> -Kame
>