Re: [RFCv2 1/6] mm: introduce MADV_COLD

On Tue 04-06-19 13:26:51, Minchan Kim wrote:

On Mon, Jun 03, 2019 at 09:16:07AM +0200, Michal Hocko wrote:

[...]

quoted

Right. But there is still the page cache reclaim. Is it expected that
an explicitly cold memory doesn't get reclaimed because we have a
sufficient amount of page cache (a very common case) and we never age
anonymous memory because of that?

If there are lots of used-once pages in file-LRU, I think there is no
need to reclaim anonymous pages because it needs bigger overhead due to
IO. It has been true for a long time in current VM policy.

You are making an assumption which is not universally true. If I _know_
that there is a considerable amount of idle anonymous memory then I
would really prefer if it goes to the swap rather than make a pressure
on caching. Inactive list is not guaranteed to contain only used-once
pages, right?

Anyway, as already mentioned, we can start with a simpler implementation
for now and explicitly note that pagecache biased reclaim is known to be
a problem potentially. I am pretty sure somebody will come sooner or
later and we can address the problem then with some good numbers to back
the additional complexity.

-- 
Michal Hocko
SUSE Labs