Re: OOM at low page cache?

Minchan Kim
2015-01-28T06:26:21Z

Hello,

On Tue, Jan 27, 2015 at 12:03:34PM +0100, Vlastimil Babka wrote:
> CC linux-mm in case somebody has a good answer but missed this in lkml traffic
>
> On 01/23/2015 11:18 PM, John Moser wrote:
> > Why is there no tunable to OOM at low page cache?

AFAIR, there were several trial although there wasn't acceptable
at that time. One thing I can remember is min_filelist_kbytes.
FYI, http://lwn.net/Articles/412313/

> >
> > I have no swap configured. I have 16GB RAM. If Chrome or Gimp or some
> > other stupid program goes off the deep end and eats up my RAM, I hit
> > some 15.5GB or 15.75GB usage and stay there for about 40 minutes. Every
> > time the program tries to do something to eat more RAM, it cranks disk
> > hard; the disk starts thrashing, the mouse pointer stops moving, and
> > nothing goes on. It's like swapping like crazy, except you're reading
> > library files instead of paged anonymous RAM.
> >
> > If only I could tell the system to OOM kill at 512MB or 1GB or 95%
> > non-evictable RAM, it would recover on its own. As-is, I need to wait
> > or trigger the OOM killer by sysrq.
> >
> > Am I just the only person in the world who's ever had that problem? Or
> > is it a matter of questions fast popping up when you try to do this
> > *and* enable paging to disk? (In my experience, that's a matter of too
> > much swap space: if you have 16GB RAM and your computer dies at 15.25GB
> > usage, your swap space should be no larger than 750MB plus inactive
> > working RAM; obviously, your computer can't handle paging 750MB back and
> > forth. If you make it 8GB wide and you start swap thrashing at 2GB
> > usage, you have too much swap available).
> >
> > I guess you could try to detect excessive swap and page cache thrashing,
> > but that's complex; if anyone really wanted to do that, it would be done
> > by now. A low-barrier OOM is much simpler.

I'm far away from reclaim code for a long time but when I read again,
I found something strange.

With having swap in get_scan_count, we keep a mount of file LRU + free
as above than high wmark to prevent file LRU thrashing but we don't
with no swap. Why?

Anyway, I believe we should fix it and we now have workingset.c so
there might be more ways to be smart than old(although I am concern
about that shadow shrinker blows out lots of information to be useful
to detect in heavy memory pressure like page thrashing)

Below could be band-aid until we find a elegant solution?

>From c51787f7d75340b54bab2b5e3c587f4a483da51a Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Wed, 28 Jan 2015 14:01:57 +0900
Subject: [PATCH] mm: prevent page thrashing

No-Signed-off-by: Minchan Kim <minchan@kernel.org>
---
mm/vmscan.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 671e47edb584..b258df552e3a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2143,6 +2143,25 @@ out:
denominator);
break;
case SCAN_FILE:
+ if (file && global_reclaim(sc)) {
+ unsigned long zonefile;
+ unsigned long zonefree;
+
+ zonefree = zone_page_state(zone,
+ NR_FREE_PAGES);
+ zonefile = zone_page_state(zone,
+ NR_ACTIVE_FILE) +
+ zone_page_state(zone,
+ NR_INACTIVE_FILE);
+
+ /* OOM is better than code thrashing */
+ if (zonefile + zonefree <=
+ high_wmark_pages(zone)) {
+ size = 0;
+ scan = 0;
+ }
+ break;
+ }
case SCAN_ANON:
/* Scan one type exclusively */
if ((scan_balance == SCAN_FILE) != file) {
--
1.9.1

--
Kind regards,
Minchan Kim