Re: [RFC PATCH] mm, memcg: fix (Re: OOM: Better, but still there on)

On Thu, Dec 29, 2016 at 10:04:32AM +0100, Michal Hocko wrote:

On Thu 29-12-16 10:20:26, Minchan Kim wrote:

quoted

On Tue, Dec 27, 2016 at 04:55:33PM +0100, Michal Hocko wrote:

quoted

Hi,
could you try to run with the following patch on top of the previous
one? I do not think it will make a large change in your workload but
I think we need something like that so some testing under which is known
to make a high lowmem pressure would be really appreciated. If you have
more time to play with it then running with and without the patch with
mm_vmscan_direct_reclaim_{start,end} tracepoints enabled could tell us
whether it make any difference at all.

I would also appreciate if Mel and Johannes had a look at it. I am not
yet sure whether we need the same thing for anon/file balancing in
get_scan_count. I suspect we need but need to think more about that.

Thanks a lot again!
---
From b51f50340fe9e40b68be198b012f8ab9869c1850 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.com>
Date: Tue, 27 Dec 2016 16:28:44 +0100
Subject: [PATCH] mm, vmscan: consider eligible zones in get_scan_count

get_scan_count considers the whole node LRU size when
- doing SCAN_FILE due to many page cache inactive pages
- calculating the number of pages to scan

in both cases this might lead to unexpected behavior especially on 32b
systems where we can expect lowmem memory pressure very often.

A large highmem zone can easily distort SCAN_FILE heuristic because
there might be only few file pages from the eligible zones on the node
lru and we would still enforce file lru scanning which can lead to
trashing while we could still scan anonymous pages.

Nit:
It doesn't make thrashing because isolate_lru_pages filter out them
but I agree it makes pointless CPU burning to find eligible pages.

This is not about isolate_lru_pages. The trashing could happen if we had
lowmem pagecache user which would constantly reclaim recently faulted
in pages while there is anonymous memory in the lowmem which could be
reclaimed instead.
 
[...]

quoted

quoted

 /*
+ * Return the number of pages on the given lru which are eligibne for the

                                                            eligible

fixed

quoted

quoted

+ * given zone_idx
+ */
+static unsigned long lruvec_lru_size_zone_idx(struct lruvec *lruvec,
+		enum lru_list lru, int zone_idx)

Nit:

Although there is a comment, function name is rather confusing when I compared
it with lruvec_zone_lru_size.

I am all for a better name.

quoted

lruvec_eligible_zones_lru_size is better?

this would be too easy to confuse with lruvec_eligible_zone_lru_size.
What about lruvec_lru_size_eligible_zones?

Don't mind.

quoted

Nit:

With this patch, inactive_list_is_low can use lruvec_lru_size_zone_idx rather than
own custom calculation to filter out non-eligible pages. 

Yes, that would be possible and I was considering that. But then I found
useful to see total and reduced numbers in the tracepoint
http://lkml.kernel.org/r/20161228153032.10821-8-mhocko@kernel.org
and didn't want to call lruvec_lru_size 2 times. But if you insist then
I can just do that.

I don't mind either but I think we need to describe the reason if you want to
go with your open-coded version. Otherwise, someone will try to fix it.

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