2 Dec
2017
2 Dec
'17
5:09 a.m.
On Fri, Dec 01, 2017 at 11:03:02PM +0000, Ralph Corderoy wrote:
Hi Larry,
Is that because the pages have been dirty for so long they've reached
the VM-writeback timeout even though there's no pressure to use them for
something else? Or has that been lengthened because you don't fear
power loss wiping volatile RAM?
I'm tinkering with the pageout daemon so I'm trying to apply memory
pressure. I have 10 25GB processes (25GB malloced) and the processes just
walk the memory over and over. This is on a 256GB main memory machine
(2 socket haswell, 28 cpus, 28 1TB SSDs, on loan from Netflix).
It's the old "10 pounds of shit in a 5 pound bag" problem, same old stuff,
just a bigger bag.
The problem is that OOM can't kill the processes that are the problem,
they are stuck in disk wait. That's why I started asking why can't you
kill a process that's in the middle of I/O.
So OOM
code kills a (random) process in hopes of freeing up some
pages but if this process is stuck in diskIO, nothing can be freed
and everything grinds to a halt.
Yep, exactly.