Re: [Bug 107771] New: Single process tries to use more than 1/2 physical RAM, OS starts thrashing

[Rik van Riel <riel@redhat.com>]

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On Fri, 2016-04-15 at 12:15 -0700, Andrew Morton wrote:
> (switched to email.  Please respond via emailed reply-to-all, not via
> the
> bugzilla web interface).
> 
> This is ... interesting.

First things first. What is the value of
/proc/sys/vm/zone_reclaim?

I am assuming this is a two socket system,
with two 12-core CPUs. Am I right?

> On Thu, 12 Nov 2015 18:46:35 +0000 bugzilla-
> daemon@bugzilla.kernel.org wrote:
> 
> > 
> > https://bugzilla.kernel.org/show_bug.cgi?id=107771
> > 
> >             Bug ID: 107771
> >            Summary: Single process tries to use more than 1/2
> > physical
> >                     RAM, OS starts thrashing
> >            Product: Memory Management
> >            Version: 2.5
> >     Kernel Version: 4.3.0-040300-generic (Ubuntu)
> >           Hardware: All
> >                 OS: Linux
> >               Tree: Mainline
> >             Status: NEW
> >           Severity: normal
> >           Priority: P1
> >          Component: Page Allocator
> >           Assignee: akpm@linux-foundation.org
> >           Reporter: theosib@gmail.com
> >         Regression: No
> > 
> > I have a 24-core (48 thread) system with 64GB of RAM.  
> > 
> > When I run multiple processes, I can use all of physical RAM before
> > swapping
> > starts.  However, if I'm running only a *single* process, the
> > system will start
> > swapping after I've exceeded only 1/2 of available physical
> > RAM.  Only after
> > swap fills does it start using more of the physical RAM.  
> > 
> > I can't find any ulimit settings or anything else that would cause
> > this to
> > happen intentionally. 
> > 
> > I had originally filed this against Ubuntu, but I'm now running a
> > more recent
> > kernel, and the problem persists, so I think it's more appropriate
> > to file
> > here.  There are some logs that they had me collect, so if you want
> > to see
> > them, the are here:
> > 
> > https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1513673
> > 
> > I don't recall this problem happening with older kernels (whatever
> > came with
> > Ubuntu 15.04), although I may just not have noticed.  By swapping
> > early, I'm
> > limited by the speed of my SSD, which is moving only about 20MB/sec
> > in each
> > direction, and that makes what I'm running take 10 times as long to
> > complete.
> > 
-- 
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