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    SubjectRe: [PATCH 4/6] Have x86_64 use add_active_range() and free_area_init_nodes
    Mel Gorman wrote:
    > On Thu, 31 Aug 2006, Mika Penttilä wrote:
    >
    >>
    >>>>> static __init inline int srat_disabled(void)
    >>>>> @@ -166,7 +167,7 @@ static int hotadd_enough_memory(struct b
    >>>>>
    >>>>> if (mem < 0)
    >>>>> return 0;
    >>>>> - allowed = (end_pfn - e820_hole_size(0, end_pfn)) * PAGE_SIZE;
    >>>>> + allowed = (end_pfn - absent_pages_in_range(0, end_pfn)) *
    >>>>> PAGE_SIZE;
    >>>>> allowed = (allowed / 100) * hotadd_percent;
    >>>>> if (allocated + mem > allowed) {
    >>>>> unsigned long range;
    >>>>> @@ -238,7 +239,7 @@ static int reserve_hotadd(int node, unsi
    >>>>> }
    >>>>>
    >>>>> /* This check might be a bit too strict, but I'm keeping it
    >>>>> for now. */
    >>>>> - if (e820_hole_size(s_pfn, e_pfn) != e_pfn - s_pfn) {
    >>>>> + if (absent_pages_in_range(s_pfn, e_pfn) != e_pfn - s_pfn) {
    >>>>> printk(KERN_ERR "SRAT: Hotplug area has existing
    >>>>> memory\n");
    >>>>> return -1;
    >>>>> }
    >>>>>
    >>>> We really do want to to compare against the e820 map at it contains
    >>>> the memory that is really present (this info was blown away before
    >>>> acpi_numa)
    >>>
    >>> The information used by absent_pages_in_range() should match what was
    >>> available to e820_hole_size().
    >>>
    >>>
    >> But it doesn't : all active ranges are removed before parsing srat. I
    >> think we really need to check against e820 here.
    >>
    >
    > What I see happening is this;
    >
    > 1. setup_arch calls e820_register_active_regions(0, 0, -1UL) so that all
    > regions are registered as if they were on node 0 so e820_end_of_ram()
    > gets the right value
    > 2. remove_all_active_regions() is called to clear what was registered so
    > that rediscovery with NUMA awareness happens
    > 3. acpi_numa_init() is called. It parses the table and a little later
    > calls acpi_numa_memory_affinity_init() for each range in the table so
    > now we're into x86_64 code
    > 4. acpi_numa_memory_affinity_init() basically deals an address range.
    > Assuming the SRAT table is not broken, it calls
    > e820_register_active_ranges() for that range. At this point, for the
    > range of addresses, the active ranges are now registered
    > 5. reserve_hotadd is called if the range is hotpluggable. It will fail if
    > it finds that memory already exists there
    >
    > So, when absent_pages_in_range() is being called by reserve_hotadd(),
    > it should be using the same information that was available in e820.
    > What am I missing?
    >
    Ok, right, missed the e820_register_active_ranges() in
    acpi_numa_memory_affinity_init() before reserve_hotadd stuff. So
    logically it should be working mod bugs.

    Argh, just looked through the reserve hotadd code and
    hotadd_enough_memory() looks still broken. And why are we doing
    reserve_bootmem_node(), the regions aren't present RAM anyways?

    --Mika

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