linux-kernel - Re: question about link_mem

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Date:	Mon, 12 Dec 2011 14:11:28 +0100
From:	Kay Sievers <kay.sievers@...y.org>
To:	Robin Holt <holt@....com>
Cc:	Greg Kroah-Hartmann <greg@...ah.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: question about link_mem_sections()

On Mon, Dec 12, 2011 at 13:45, Robin Holt <holt@....com> wrote:
> On Mon, Dec 12, 2011 at 01:35:50PM +0100, Kay Sievers wrote:
>> you added find_memory_block_hinted() with:
>>   http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=63d027a63888e993545d10fdfe4107d543f01bca
>>
>> I try to understand what's going on here, because we need to switch
>> away from 'struct sysdev'.
>>
>> In the loop over the node data you call find_memory_block_hinted() in
>> a row, which might all take a reference. At the end of the section you
>> drop only the last reference of the iteration. The code before your
>> change dropped all references inside the loop.
>>
>> Could you please explain the intended behaviour?
>>
>> If all is right, we should at least move the now wrong comment where is belongs.
>
> Take a look at that commit's parent's parent:
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commit;h=c25d1dfbd403209025df41a737f82ce8f43d93f5
>
> This adds the kset_find_obj_hinted() function.  That function expects
> the kobject_get to have already been done on the object passed in and
> will release that reference when it advances to the next object.
>
> Within the loop of the link_mem_sections(), we need to retain the
> kobject_get reference between calls to find_memory_block_hinted() and
> rely upon that functions call to kset_find_obj_hinted() to release all
> but the last reference.
>
> I hope that explains things.  If not, please feel free to ping me again.

Gah, what a twisted logic. That looks more like a pretty specialized
implementation of an iterator and not a generic kobject 'find'
function, when it implicitly mangles the hint. :)

Anyway, sounds fine, only the 'dead' and misleading comment in
link_mem_sections should move out of the loop, right?

Thanks,
Kay
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