Re: OOM at low page cache?

[Vlastimil Babka <vbabka@suse.cz>]

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?
> 
> 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.
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