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SubjectRe: [PATCH 5/5] mm: clear N_HIGH_MEMORY map before se set it again -v2
On Thu, 14 May 2009 10:05:43 -0700
Yinghai Lu <yinghai@kernel.org> wrote:

> Andrew Morton wrote:
> > On Thu, 14 May 2009 09:43:22 -0700
> > Yinghai Lu <yinghai@kernel.org> 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()?

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.


> >
> >> Signed-off-by: Yinghai Lu <Yinghai@kernel.org>
> >> Tested-by: Jack Steiner <steiner@sgi.com>
> >
> > 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.



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