linux-kernel - Re: question about link_mem

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Date:	Mon, 12 Dec 2011 06:45:38 -0600
From:	Robin Holt <holt@....com>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Robin Holt <holt@....com>, 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 01:35:50PM +0100, Kay Sievers wrote:
> Robin,
> 
> 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.

Thanks,
Robin
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