Re: OOM at low page cache?

Vlastimil Babka
2015-01-27T11:03:39Z

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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