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    SubjectRe: [PATCH 2 of 4] hotplug-memory: adding non-section-aligned memory is bad
    KAMEZAWA Hiroyuki wrote:
    > On Fri, 28 Mar 2008 10:34:51 +0900
    > Yasunori Goto <y-goto@jp.fujitsu.com> wrote:
    >
    >>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
    >>>> --- a/mm/memory_hotplug.c
    >>>> +++ b/mm/memory_hotplug.c
    >>>> @@ -300,6 +300,11 @@
    >>>> int ret;
    >>>> u64 start = res->start;
    >>>> u64 size = res->end - res->start + 1;
    >>>> +
    >>>> + /* Adding non-section-aligned memory will give unexpected
    >>>> + and unintuitive results. */
    >>>> + WARN_ON((start & SECTION_SIZE_MASK) != 0);
    >>>> + WARN_ON((size & SECTION_SIZE_MASK) != 0);
    >>>>
    >>>>
    >>> Why just WARNING ? not BUG_ON?
    >>>
    >> Both Nack.
    >>
    >> Because, firmware may occupy some area in the section.
    >> Firmware must exclude those area to notify kernel. So, E820, EFI,
    >> or _CRS of ACPI may return not aligned address and size.
    >> register_memory_resource() and walk_memory_resource() are to skip
    >> them silently. This is intended.
    >>
    >>
    > Ah, ok. sorry.
    >
    > Jeremy, I think you can check whether you have 'struct page' or not by
    > pfn_valid().
    >
    > If pfn_valid() == false, you should call add_memory() and create
    > a section/mem_map. If pfn_valid() == true, you should just remove
    > PG_reserved bit in mem_map by online_page().

    OK. Would that ever be necessary if I explicitly align my start and size?

    J



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