linux-kernel - Re: crash in kmem_cache

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Message-ID: <20080118213011.GC10491@csn.ul.ie>
Date:	Fri, 18 Jan 2008 21:30:11 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <clameter@....com>
Cc:	Olaf Hering <olaf@...fle.de>,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Linux MM <linux-mm@...ck.org>
Subject: Re: crash in kmem_cache_init

On (18/01/08 10:47), Christoph Lameter didst pronounce:
> On Thu, 17 Jan 2008, Olaf Hering wrote:
> 
> > early_node_map[1] active PFN ranges
> >     1:        0 ->   892928
> > Could not find start_pfn for node 0
> 
> Corrupted min_pfn?
> 

Doubtful. Node 0 has no memory but it is still being initialised.

Still, I looked closer at what is going on when that message gets
displayed and I see this in free_area_init_nodes()

        for_each_online_node(nid) {
                pg_data_t *pgdat = NODE_DATA(nid);
                free_area_init_node(nid, pgdat, NULL,
                                find_min_pfn_for_node(nid), NULL);

                /* Any memory on that node */
                if (pgdat->node_present_pages)
                        node_set_state(nid, N_HIGH_MEMORY);
                check_for_regular_memory(pgdat);
        }

This "Any memory on that node" thing is new and it says if there is any
memory on the node, set N_HIGH_MEMORY. Fine I guess, I haven't tracked these
changes closely. It calls check_for_regular_memory() which looks like

static void check_for_regular_memory(pg_data_t *pgdat)
{
#ifdef CONFIG_HIGHMEM
        enum zone_type zone_type;

        for (zone_type = 0; zone_type <= ZONE_NORMAL; zone_type++) {
                struct zone *zone = &pgdat->node_zones[zone_type];
                if (zone->present_pages)
                        node_set_state(zone_to_nid(zone), N_NORMAL_MEMORY);
        }
#endif
}

i.e. go through the other zones and if any of them have memory, set
N_NORMAL_MEMORY. But... it only does this on CONFIG_HIGHMEM which on
PPC64 is not going to be set so N_NORMAL_MEMORY never gets set on
POWER.... That sounds bad.

mel@...old:~/git/linux-2.6/mm$ grep -n N_NORMAL_MEMORY slab.c 
1593:           for_each_node_state(nid, N_NORMAL_MEMORY) {
1971:   for_each_node_state(node, N_NORMAL_MEMORY) {
2102:                   for_each_node_state(node, N_NORMAL_MEMORY) {
3818:   for_each_node_state(node, N_NORMAL_MEMORY) {

and one of them is in kmem_cache_init(). That seems very significant.
Christoph, can you think of possibilities of where N_NORMAL_MEMORY not
being set would cause trouble for slab?

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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