linux-kernel - RE: [PATCH 0/3] mm: Randomize free memory

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Date:   Fri, 21 Sep 2018 23:48:18 +0000
From:   "Elliott, Robert (Persistent Memory)" <elliott@....com>
To:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     Dan Williams <dan.j.williams@...el.com>,
        "Hocko, Michal" <MHocko@...e.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Kani, Toshi" <toshi.kani@....com>
Subject: RE: [PATCH 0/3] mm: Randomize free memory


> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org <linux-kernel-
> owner@...r.kernel.org> On Behalf Of Kees Cook
> Sent: Friday, September 21, 2018 2:13 PM
> Subject: Re: [PATCH 0/3] mm: Randomize free memory
...
> I'd be curious to hear more about the mentioned cache performance
> improvements. I love it when a security feature actually _improves_
> performance. :)

It's been a problem in the HPC space:
http://www.nersc.gov/research-and-development/knl-cache-mode-performance-coe/

A kernel module called zonesort is available to try to help:
https://software.intel.com/en-us/articles/xeon-phi-software

and this abandoned patch series proposed that for the kernel:
https://lkml.org/lkml/2017/8/23/195

Dan's patch series doesn't attempt to ensure buffers won't conflict, but
also reduces the chance that the buffers will. This will make performance
more consistent, albeit slower than "optimal" (which is near impossible
to attain in a general-purpose kernel).  That's better than forcing
users to deploy remedies like:
    "To eliminate this gradual degradation, we have added a Stream
     measurement to the Node Health Check that follows each job;
     nodes are rebooted whenever their measured memory bandwidth
     falls below 300 GB/s."

---
Robert Elliott, HPE Persistent Memory