linux-kernel - crashkernel only allowing smaller allocations as kernel version increases

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAANLjFrWDNaoopgeh6V_tY9arPsREpMbtsLzURiMOg0rgRMW0g@mail.gmail.com>
Date:   Thu, 8 Dec 2016 11:36:03 -0700
From:   Robert LeBlanc <robert@...lancnet.us>
To:     "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: crashkernel only allowing smaller allocations as kernel version increases

I've been trying to capture a core to help in debuging a problem, but
it seems that as I go up in kernel versions, I can only allocate less
and less memory to crashkernel and with 4.9-rc8 I can't allocate
enough to prevent OOM (specifically on CentOS with iSCSI root). I'm
seeing the same reduction of allocatable memory on both Debian and
CentOS on the same hardware

As an example:
Debian
3.16 - 1 GB is OK
4.9-rc7 - ~512MB is OK, but gets "kernel version is not supported".

CentOS
3.10 - 1 GB is OK
4.8 - ~800MB is OK
4.9-rc8 - ~512MB is OK, but OOMs

CentOS 4.9 kernel was built with default config, Debian 4.9 was built
by coping the distro 3.16.0-4 config and then running make menuconfig.

Trying to specify memory amount above this causes kdump to report that
no memory has been reserved. The hardware has 512GB of RAM. Am I
missing some config option that limiting how much crashkernel can
reserve?

I also verified on my test desktop with 8GB of RAM that setting
crashkernel=1024M also fails to allocate memory with 4.9-rc8, but
works fine with 128M for instance.

Thanks,

----------------
Robert LeBlanc
PGP Fingerprint 79A2 9CA4 6CC4 45DD A904  C70E E654 3BB2 FA62 B9F1