Re: OOM at low page cache?

[Minchan Kim]

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?