linux-kernel - Re: [Patch](memory hotplug)Allocate usemap on the section with pgdat (take 2)

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Date:	Mon, 16 Jun 2008 22:22:53 +0900
From:	Yasunori Goto <y-goto@...fujitsu.com>
To:	Andy Whitcroft <apw@...dowen.org>
Cc:	David Miller <davem@...emloft.net>,
	Badari Pulavarty <pbadari@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Hiroyuki KAMEZAWA <kamezawa.hiroyu@...fujitsu.com>,
	Tony Breeds <tony@...eyournoodle.com>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, Mel Gorman <mel@....ul.ie>
Subject: Re: [Patch](memory hotplug)Allocate usemap on the section with pgdat (take 2)

> > +static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
> > +{
> > +	unsigned long usemap_snr, pgdat_snr;
> > +	static unsigned long old_usemap_snr = NR_MEM_SECTIONS;
> > +	static unsigned long old_pgdat_snr = NR_MEM_SECTIONS;
> > +	struct pglist_data *pgdat = NODE_DATA(nid);
> > +	int usemap_nid;
> > +
> > +	usemap_snr = pfn_to_section_nr(__pa(usemap) >> PAGE_SHIFT);
> > +	pgdat_snr = pfn_to_section_nr(__pa(pgdat) >> PAGE_SHIFT);
> > +	if (usemap_snr == pgdat_snr)
> > +		return;
> > +
> > +	if (old_usemap_snr == usemap_snr && old_pgdat_snr == pgdat_snr)
> > +		/* skip redundant message */
> > +		return;
> > +
> > +	old_usemap_snr = usemap_snr;
> > +	old_pgdat_snr = pgdat_snr;
> 
> The pgdat and usemap sections are node specific, but this repeat message
> check is not, so if I add sections alternatly to node 0 and node 1 I
> will recieve the warning for every addition?

Yes. alloc_bootmem_section() may be failed, and usemap may be allocated on
other node. I would like to notice for its dependency case too.

> 
> > +
> > +	usemap_nid = sparse_early_nid(__nr_to_section(usemap_snr));
> > +	if (usemap_nid != nid) {
> > +		printk("node %d must be removed before remove section %ld\n",
> > +		       nid, usemap_snr);
> > +		return;
> > +	}
> > +	/*
> > +	 * There is a dependency deadlock.
> > +	 * Some platforms allow un-removable section because they will just
> > +	 * gather other removable sections for dynamic partitioning.
> > +	 * Just notify un-removable section's number here.
> > +	 */
> > +	printk(KERN_INFO "section %ld and %ld", usemap_snr, pgdat_snr);
> > +	printk(" can't be hotremoved due to dependency each other.\n");
> 
> This might be better worded as a circular dependancy.  Also it would be
> nice to include the node perhaps:
> 
> 	"Sections %ld and %ld (node %ld) have a circular dependancy on
> 	usemap and pgdat allocations"

Thanks. I'll change it.


-- 
Yasunori Goto 


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