Re: [RFC][PATCH 0/3] page cgroup diet

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

(2012/03/20 4:59), Konstantin Khlebnikov wrote:

> KAMEZAWA Hiroyuki wrote:
>> This is just an RFC...test is not enough yet.
>>
>> I know it's merge window..this post is just for sharing idea.
>>
>> This patch merges pc->flags and pc->mem_cgroup into a word. Then,
>> memcg's overhead will be 8bytes per page(4096bytes?).
>>
>> Because this patch will affect all memory cgroup developers, I'd like to
>> show patches before MM Summit. I think we can agree the direction to
>> reduce size of page_cgroup..and finally integrate into 'struct page'
>> (and remove cgroup_disable= boot option...)
>>
>> Patch 1/3 - introduce pc_to_mem_cgroup and hide pc->mem_cgroup
>> Patch 2/3 - remove pc->mem_cgroup
>> Patch 3/3 - remove memory barriers.
>>
>> I'm now wondering when this change should be merged....
>>
> 
> This is cool, but maybe we should skip this temporary step and merge all this stuff into page->flags.


Why we should skip and delay reduction of size of page_cgroup
which is considered as very big problem ? 

> I think we can replace zone-id and node-id in page->flags with cumulative dynamically allocated lruvec-id,
> so there will be enough space for hundred cgroups even on 32-bit systems.


Where section-id  is ?
IIUC, now, page->section->zone/node is calculated if CONFIG_SPARSEMEM.

BTW, I doubt that we can modify page->flags dynamically with multi-bit operations...using
cmpxchg per each page when it's charged/uncharged/other ?

> 
> After lru_lock splitting page to lruvec translation will be much frequently used than page to zone,
> so page->zone and page->node translations can be implemented as page->lruvec->zone and page->lruvec->node.
> 

And need to take rcu_read_lock() around page_zone() ?

Thanks,
-Kame



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