From: david@lang.hm
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
Cyrill Gorcunov <gorcunov@gmail.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Pavel Emelyanov <xemul@parallels.com>,
Andrey Vagin <avagin@openvz.org>, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>,
Glauber Costa <glommer@parallels.com>,
Andi Kleen <andi@firstfloor.org>, Tejun Heo <tj@kernel.org>,
Matt Helsley <matthltc@us.ibm.com>,
Pekka Enberg <penberg@kernel.org>,
Eric Dumazet <eric.dumazet@gmail.com>,
Vasiliy Kulikov <segoon@openwall.com>,
Andrew Morton <akpm@linux-foundation.org>,
Valdis.Kletnieks@vt.edu
Subject: Re: [RFC] syscalls, x86: Add __NR_kcmp syscall
Date: Wed, 18 Jan 2012 14:05:31 -0800 (PST) [thread overview]
Message-ID: <alpine.DEB.2.02.1201181404480.6780@asgard.lang.hm> (raw)
In-Reply-To: <m1obu29fnf.fsf@fess.ebiederm.org>
On Tue, 17 Jan 2012, Eric W. Biederman wrote:
> "H. Peter Anvin" <hpa@zytor.com> writes:
>
>> On 01/17/2012 06:44 AM, Cyrill Gorcunov wrote:
>>> On Tue, Jan 17, 2012 at 04:38:14PM +0200, Alexey Dobriyan wrote:
>>>> On 1/17/12, Cyrill Gorcunov <gorcunov@gmail.com> wrote:
>>>>> +#define KCMP_EQ 0
>>>>> +#define KCMP_LT 1
>>>>> +#define KCMP_GT 2
>>>>
>>>> LT and GT are meaningless.
>>>>
>>>
>>> I found symbolic names better than open-coded values. But sure,
>>> if this is problem it could be dropped.
>>>
>>> Or you mean that in general anything but 'equal' is useless?
>>>
>>
>> Why on Earth would user space need to know which order in memory certain
>> kernel objects are?
>
> For checkpoint restart and for some other kinds of introspection what is
> needed is a comparison function to see if two processes share the same
> object. The most interesting of these objects from a checkpoint restart case
> are file descriptors, and there can be a lot of file descriptors.
>
> The order in memory does not matter. What does matter is that the
> comparison function return some ordering between objects. The algorithm
> for figuring out of N items which of them are duplicates is O(N^2) if
> the comparison function can only return equal or not equal. The
> algorithm for finding duplications is only O(NlogN) if the comparison
> function will return an ordering among the objects.
so what you really want is a syscall that can take a list of objects
instead of having to do a syscall per object. right?
David Lang
next prev parent reply other threads:[~2012-01-18 22:07 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-17 14:27 [RFC] syscalls, x86: Add __NR_kcmp syscall Cyrill Gorcunov
2012-01-17 14:38 ` Alexey Dobriyan
2012-01-17 14:44 ` Cyrill Gorcunov
2012-01-17 18:47 ` H. Peter Anvin
2012-01-17 21:15 ` Cyrill Gorcunov
2012-01-17 21:40 ` Eric W. Biederman
2012-01-18 5:07 ` Pavel Emelyanov
2012-01-17 21:35 ` Eric W. Biederman
2012-01-18 8:01 ` Cyrill Gorcunov
2012-01-18 9:12 ` KOSAKI Motohiro
2012-01-18 9:19 ` Pavel Emelyanov
2012-01-18 9:23 ` KOSAKI Motohiro
2012-01-18 11:57 ` Cyrill Gorcunov
2012-01-18 16:46 ` KOSAKI Motohiro
2012-01-18 17:20 ` Cyrill Gorcunov
2012-01-18 22:05 ` david [this message]
2012-01-18 22:49 ` Cyrill Gorcunov
2012-01-18 23:29 ` Eric W. Biederman
2012-01-19 6:55 ` Cyrill Gorcunov
2012-01-20 3:16 ` Eric W. Biederman
2012-01-20 8:40 ` Cyrill Gorcunov
2012-01-20 9:02 ` Cyrill Gorcunov
2012-01-20 14:51 ` H. Peter Anvin
2012-01-20 16:29 ` Cyrill Gorcunov
2012-01-20 16:57 ` H. Peter Anvin
2012-01-20 18:19 ` Cyrill Gorcunov
2012-01-20 18:22 ` Cyrill Gorcunov
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