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crashkernel=xM tries to reserve memory for the crash kernel under 4G, which is enough, usually. But this could fail sometimes, for example when one tries to reserve a big chunk like 2G, for example. So let the crashkernel=xM just fall back to use high memory in case it fails to find a suitable low range. Do not set the ,high as default because it allocates extra low memory for DMA buffers and swiotlb, and this is not always necessary for all machines. Typically, crashkernel=128M usually works with low reservation under 4G, so keep <4G as default. [ bp: Massage. ] Signed-off-by: Dave Young <dyoung@redhat.com> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Ingo Molnar <mingo@kernel.org> Acked-by: Baoquan He <bhe@redhat.com> Cc: Dave Young <dyoung@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Eric Biederman <ebiederm@xmission.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Juergen Gross <jgross@suse.com> Cc: Kees Cook <keescook@chromium.org> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: linux-doc@vger.kernel.org Cc: "Paul E. McKenney" <paulmck@linux.ibm.com> Cc: Petr Tesarik <ptesarik@suse.cz> Cc: piliu@redhat.com Cc: Ram Pai <linuxram@us.ibm.com> Cc: Sinan Kaya <okaya@codeaurora.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Thymo van Beers <thymovanbeers@gmail.com> Cc: vgoyal@redhat.com Cc: x86-ml <x86@kernel.org> Cc: Yinghai Lu <yinghai@kernel.org> Cc: Zhimin Gu <kookoo.gu@intel.com> Link: https://lkml.kernel.org/r/20190422031905.GA8387@dhcp-128-65.nay.redhat.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.