yinghai at kernel
May 14, 2009, 10:34 AM
Post #5 of 6
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Re: [PATCH 5/5] mm: clear N_HIGH_MEMORY map before se set it again -v2
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Andrew Morton wrote:
> On Thu, 14 May 2009 10:05:43 -0700
> Yinghai Lu <yinghai [at] kernel> wrote:
>
>> Andrew Morton wrote:
>>> On Thu, 14 May 2009 09:43:22 -0700
>>> Yinghai Lu <yinghai [at] kernel> wrote:
>>>
>>>> incase some system strange SRAT table. some kind of small range.
>>>> or with mem= etc
>>>>
>>> That description is very hard to understand. Please provide more details.
>> if the wrong SRAT table, have small range for some node. that node will not be onlined.
>> In the early checking, the bit in node_states[N_HIGH_MEMORY] for the node is set even
>> that node has less RAM like 1M, and it is not cleared before the bit is set again in
>> the following loop according online nodes.
>
> Where in the kernel does this setting of the bit in node_states[]
> occur? early_calculate_totalpages()?
yes.
>
> Where in the kernel is it later decided to _not_ use these pages in
> that node? Perhaps that's the place where the problem should be fixed.
in free_area_init_nodes()
/* Initialise every node */
mminit_verify_pageflags_layout();
setup_nr_node_ids();
for_each_online_node(nid) {
pg_data_t *pgdat = NODE_DATA(nid);
free_area_init_node(nid, 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);
}
so that patch clear that node_mask before set those bits according if that node is online
and node_present_pages is there.
>
>
>>>> Signed-off-by: Yinghai Lu <Yinghai [at] kernel>
>>>> Tested-by: Jack Steiner <steiner [at] sgi>
>>> What reason did Jack have to test this? Perhaps he hit some bug?
>>> If so, please fully describe that bug in the changelog.
>> for some memmoryless node and strange memmap.
>
> That's not a very good problem description.
>
> Put yourself in the position of a distro engineer whose customer
> reports a 2.6.26 problem. He's going to look at your patch wondering
> whether it might fix his customer's problem. We should provide him
> with sufficient information to be able to determine this.
>
>>>
>>>> Index: linux-2.6/mm/page_alloc.c
>>>> ===================================================================
>>>> --- linux-2.6.orig/mm/page_alloc.c
>>>> +++ linux-2.6/mm/page_alloc.c
>>>> @@ -4041,6 +4047,11 @@ void __init free_area_init_nodes(unsigne
>>>> early_node_map[i].start_pfn,
>>>> early_node_map[i].end_pfn);
>>>>
>>>> + /*
>>>> + * find_zone_movable_pfns_for_nodes/early_calculate_totalpages init
>>>> + * that node_mask, clear it at first
>>>> + */
>>>> + nodes_clear(node_states[N_HIGH_MEMORY]);
>>>> /* Initialise every node */
>>>> mminit_verify_pageflags_layout();
>>>> setup_nr_node_ids();
>>> If CONFIG_HIGHMEM=n, this will clear the N_NORMAL_MEMORY entry in
>>> node_states[]. Why is this correct and desirable?
>> then N_NORMAL_MEMORY == N_HIGH_MEMORY
>
> I know.
>
> But it's unobvious that this change is correct and desirable with both
> CONFIG_HIGHMEM=n and CONFIG_HIGHMEM=y.
use ifdef ?
YH
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