On 4/6/2010 3:08 PM, Russell King - ARM Linux wrote:
1. are you enabling ARCH_HAS_HOLES_MEMORYMODEL ?
Yes, although this does not impact the problem I'm dealing with. That
option is only used for /proc/pagetypeinfo currently. It would be good
if we could consolidate ARCH_HAS_HOLES_MEMORYMODEL and HOLES_IN_ZONE,
but that may be out of scope for this change.
2. where does it try to access these page structs without trying
pfn_valid() to check whether a page struct exists first?
The specific piece of code that is causing crashes in my scenario is in
vm/page_alloc.c:move_freepages(), called from move_freepages_block().
The code in move_freepages_block aligns the end_pfn to the closest page
block, which may take us to invalid memmap entries.
The macro that conditionally saves us in this case is the
pfn_valid_within(), called from move_freepages(). If HOLES_IN_ZONE is
configured, this option calls down to pfn_valid() to make sure the page
has a valid memmap entry. There are likely other cases where this is an
issue as well that I haven't run into.
Michael
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