* KAMEZAWA Hiroyuki [off-list ref] [2009-08-19 23:18:01]:

Wu Fengguang ?$B$5$s$O=q$-$^$7$?!'

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On Tue, Aug 18, 2009 at 11:57:52PM +0800, KOSAKI Motohiro wrote:

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This one of the reasons why we unconditionally deactivate
the active anon pages, and do background scanning of the
active anon list when reclaiming page cache pages.

We want to always move some pages to the inactive anon
list, so it does not get too small.

Right, the current code tries to pull inactive list out of
smallish-size state as long as there are vmscan activities.

However there is a possible (and tricky) hole: mem cgroups
don't do batched vmscan. shrink_zone() may call shrink_list()
with nr_to_scan=1, in which case shrink_list() _still_ calls
isolate_pages() with the much larger SWAP_CLUSTER_MAX.

It effectively scales up the inactive list scan rate by 10 times when
it is still small, and may thus prevent it from growing up for ever.

In that case, LRU becomes FIFO.

Jeff, can you confirm if the mem cgroup's inactive list is small?
If so, this patch should help.

This patch does right thing.
However, I would explain why I and memcg folks didn't do that in past
days.

Strangely, some memcg struct declaration is hide in *.c. Thus we can't
make inline function and we hesitated to introduce many function calling
overhead.

So, Can we move some memcg structure declaration to *.h and make
mem_cgroup_get_saved_scan() inlined function?

OK here it is. I have to move big chunks to make it compile, and it
does reduced a dozen lines of code :)

Is this big copy&paste acceptable? (memcg developers CCed).

Thanks,
Fengguang

I don't like this. plz add hooks to necessary places, at this stage.
This will be too big for inlined function, anyway.
plz move this after you find overhead is too big.

Me too.. I want to abstract the implementation within memcontrol.c to
be honest (I am concerned that someone might include memcontrol.h and
access its structure members, which scares me). Hiding it within
memcontrol.c provides the right level of abstraction.

Could you please explain your motivation for this change? I got cc'ed
on to a few emails, is this for the patch that export nr_save_scanned
approach?

-- 
	Balbir

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