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

[Andrew Morton <akpm@linux-foundation.org>]

(switched to email.  Please respond via emailed reply-to-all, not via the
bugzilla web interface).

This is ... interesting.

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.
> 
> -- 
> You are receiving this mail because:
> You are the assignee for the bug.

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