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From: "H. Peter Anvin" <hpa@zytor.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: x86@kernel.org, kexec@lists.infradead.org,
	Simon Horman <horms@verge.net.au>,
	yinghai@kernel.org, Thomas Renninger <trenn@suse.de>,
	vgoyal@redhat.com
Subject: Re: [PATCH 0/3] Cleanup kdump memmap= passing and e820 usage
Date: Wed, 30 Jan 2013 14:41:43 -0800	[thread overview]
Message-ID: <5109A1A7.1040609@zytor.com> (raw)
In-Reply-To: <87ehh2l2z3.fsf@xmission.com>

On 01/30/2013 02:29 PM, Eric W. Biederman wrote:
>>
>>> I think I would prefer that to call that new type RESERVED_MEM or
>>> RESERVED_CACHABLE.  Being more specific is fine but dumpable certainly
>>> doesn't bring to mind what we are saying.  Especially since we already
>>> communicate which areas were memory to the last kernel in an
>>> architecture generic format.
>>
>> I was thinking that marking them differently might help debugging, at
>> least, but yes, we can have a RESERVED_MEM type.
>>
>> However, Thomas does have a point that the current use of fairly small
>> positive values for Linux-defined types is a bad idea.  We should use
>> negative types, or at least something north of 0x40000000 or so.
> 
> Yes.  It doesn't much matter in the kernel but when it because part of
> the ABI it is a real issue.
> 
> Since old kernels treat any value they don't understand as reserved
> passing a modified e820 map seems reasonable to me once we have reserved
> a special linux value for it.
> 

Just to prevent the possible funnies (including collisions with -errno)
that might be caused by negative numbers, I suggest we assign
Linux-specific values starting at some huge but still positive value
like 2000000000 -- that way we avoid any possible uses of negative errno
values internally in the kernel.

The bigger question is if we need a separate value from the current
E820_RESERVED_KERN.  Since it is always easier to have multiple values
with the same semantics than it is to have too few, I would still prefer
we added a new E820_RESERVED_KDUMP, which would then be 2000000001.

What do you think?

	-hpa


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  reply	other threads:[~2013-01-30 22:41 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-01-22 15:02 [PATCH 0/3] Make use of new memmap= kernel parameter syntax Thomas Renninger
2013-01-22 15:02 ` [PATCH 1/3] kexec: Split kernel_version() to also be able to pass a release string Thomas Renninger
2013-01-22 15:02 ` [PATCH 2/3] kexec x86: Extract kernel version and convert it to KERNEL_VERSION() style Thomas Renninger
2013-01-22 15:02 ` [PATCH 3/3] kexec x86: Make kexec aware of new memmap= kernel parameter possibilities Thomas Renninger
2013-01-30  4:31 ` [PATCH 0/3] Make use of new memmap= kernel parameter syntax Simon Horman
2013-01-30  5:40   ` H. Peter Anvin
2013-01-30  5:52     ` Simon Horman
2013-01-30 16:03     ` Thomas Renninger
2013-01-30 16:06       ` [PATCH 1/3] x86 e820: Check for exactmap appearance when parsing first memmap option Thomas Renninger
2013-01-30 16:09         ` H. Peter Anvin
2013-01-30 16:08       ` [PATCH 2/3] x86: Introduce Linux kernel specific E820_RESERVED_KDUMP e820 memory range type Thomas Renninger
2013-01-30 16:10       ` [PATCH 3/3] x86 e820: Introduce memmap=kdump_reserve_usable for kdump usage Thomas Renninger
2013-01-30 16:10       ` [PATCH 0/3] Make use of new memmap= kernel parameter syntax H. Peter Anvin
2013-01-30 16:13       ` [PATCH 0/3] Cleanup kdump memmap= passing and e820 usage Thomas Renninger
2013-01-30 16:16         ` H. Peter Anvin
2013-01-30 16:39           ` Thomas Renninger
2013-01-30 16:52             ` H. Peter Anvin
2013-01-30 17:41               ` Yinghai Lu
2013-01-30 18:52               ` Eric W. Biederman
2013-01-30 21:38                 ` H. Peter Anvin
2013-01-30 21:57                   ` Eric W. Biederman
2013-01-30 22:10                     ` H. Peter Anvin
2013-01-30 22:29                       ` Eric W. Biederman
2013-01-30 22:41                         ` H. Peter Anvin [this message]
2013-01-30 22:49                           ` Yinghai Lu
2013-01-31  0:15                         ` Thomas Renninger
2013-01-31  0:18                           ` H. Peter Anvin
2013-01-31  9:11                             ` Thomas Renninger
2013-02-06 15:23                           ` Thomas Renninger
2013-02-06 23:04                             ` Eric W. Biederman
2013-02-06 23:11                               ` H. Peter Anvin
2013-02-06 23:39                                 ` Eric W. Biederman
2013-02-08 20:08                                   ` Thomas Renninger
2013-02-08 20:25                                     ` Eric W. Biederman
2013-02-08 20:56                                       ` Thomas Renninger

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