On 12/14/2012 03:37 AM, Michal Hocko wrote:

On Thu 13-12-12 23:50:30, Johannes Weiner wrote:

quoted

On Thu, Dec 13, 2012 at 10:25:43PM +0000, Satoru Moriya wrote:

quoted

I introduced swappiness check here with fe35004f because, in some 
cases, we prefer OOM to swap out pages to detect problems as soon as 
possible. Basically, we design the system not to swap out and so if 
it causes swapping, something goes wrong.

I might be missing something terribly obvious, but... why do you add 
swap space to the system in the first place?  Or in case of cgroups, 
why not set the memsw limit equal to the memory limit?

I can answer the later. Because memsw comes with its price and 
swappiness is much cheaper. On the other hand it makes sense that
swappiness==0 doesn't swap at all. Or do you think we should get back 
to _almost_ doesn't swap at all?

Right. One of the reason is what Michal described above and another
reason that I thought is softlimit. softlimit reclaim always works
with priority=0. Therefore, if we set softlimit to one memcg without
swappiness=0, the kernel scans both anonymous and filebacked pages
during soft limit reclaim for the memcg and reclaims them.

Regards,
Satoru

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