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    SubjectRe: [Patch 8/8] kexec: allow to shrink reserved memory
    KAMEZAWA Hiroyuki wrote:
    > On Mon, 17 Aug 2009 17:50:21 +0800
    > Amerigo Wang <amwang@redhat.com> wrote:
    >
    >
    >> Eric W. Biederman wrote:
    >>
    >>> Amerigo Wang <amwang@redhat.com> writes:
    >>>
    >>>
    >>>
    >>>> Not that simple, marking it as "__init" means it uses some "__init" data which
    >>>> will be dropped after initialization.
    >>>>
    >>>>
    >>> If we start with the assumption that we will be reserving to much and
    >>> will free the memory once we know how much we really need I see a very
    >>> simple way to go about this. We ensure that the reservation of crash
    >>> kernel memory is done through a normal allocation so that we have
    >>> struct page entries for every page. On 32bit x86 that is an extra 1MB
    >>> for a 128MB allocation.
    >>>
    >>> Then when it comes time to release that memory we clear whatever magic
    >>> flags we have on the page (like PG_reserve) and call free_page.
    >>>
    >>>
    >> Hmm, my MM knowledge is not good enough to judge if this works...
    >> I need to check more MM source code.
    >>
    >> Can any MM people help?
    >>
    >>
    > Hm, memory-hotplug guy is here.
    >

    Hi, thank you!
    > Can I have a question ?
    >
    > - How crash kernel's memory is preserved at boot ?
    >

    Use bootmem, I think.

    > It's hidden from the system before mem_init() ?
    >

    Not sure, but probably yes. It is reserved in setup_arch() which is
    before mm_init() which calls mem_init().

    Do you have any advice to free that reserved memory after boot? :)

    Thanks.





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