linux-kernel - Re: [PATCH] staging: Disable lustre file system for MIPS, SH, and XTENSA

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Date:	Thu, 12 Sep 2013 16:01:57 +0800
From:	Peng Tao <bergwolf@...il.com>
To:	"Dilger, Andreas" <andreas.dilger@...el.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>
Subject: Re: [PATCH] staging: Disable lustre file system for MIPS, SH, and XTENSA

On Thu, Sep 12, 2013 at 4:48 AM, Dilger, Andreas
<andreas.dilger@...el.com> wrote:
> On 2013/09/10 8:25 PM, "Peng Tao" <bergwolf@...il.com> wrote:
>
>>On Wed, Sep 11, 2013 at 9:44 AM, Christoph Hellwig <hch@...radead.org>
>>wrote:
>>> On Wed, Sep 11, 2013 at 01:14:11AM +0800, Peng Tao wrote:
>>>> The problem is access_process_vm() is not exported since certain
>>>> version of kernel including the latest. According to Christoph in the
>>>> other mail, access_process_vm() is also a core mm function that is not
>>>> supposed to be exported. Then what kind of change shall we make in
>>>> order to keep current functionality?
>>>
>>> You should remove the higher level functionality, kernel modules are
>>> not supposed to look at userspace environment variables.
>>>
>>OK. I've looked at the specific case that Lustre uses
>>access_process_vm() to get the jobid environment variable and package
>>it into the RPC requests to server. However, it turns out that in the
>>latest Lustre server code, the jobid in a request is not used
>>anywhere. So it looks like we can just get rid of it.
>>
>>Andreas, could you please confirm this? Is the jobid an obsolete
>>parameter that can be abandoned? Or is there plan to use it somehow in
>>the future?
>
> The jobid code is relatively new and in use, I'm not sure why you think
> it is not in use.  It is actually a feature that a bunch of users
> requested.
>
You are right. Sorry I misread the code yesterday. I accidentally
searched for callers of lustre_msg_get_jobid() in a kernel tree
instead of a Lustre tree. Now I see that jobid is used by server for
request tracking purpose. Thank you for pointing it out.

> The jobid feature allows tracking IO request stats for parallel user
> processes
> running on possibly thousands of different client nodes onto the servers.
> This is easy to do with a single node and a single process via PID/PPID
> and blktrace or equivalent, but otherwise impossible in a parallel
> processing
> environment where there may be users running hundreds of different jobs.
> The PID/PPID is not consistent across client nodes, and the server threads
> will randomly handle requests from all users.
>
> By all means, I'd prefer to just use access_process_vm() directly, instead
> of making a copy in the Lustre code.  Not being able to access the process
> environment seems a bit ridiculous - the kernel stores and manages this for
> the process, and it isn't even doing anything nasty like accessing the
> environment from a different process, just its own environment variables.
>
Or, can we read from /proc/self/environ? Instead of reading from
mm->env_start/env_end, we can let proc_environ_operations do the same
and avoid calling access_process_vm() directly.

Thanks,
Tao
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