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    SubjectRe: [PATCH v3 18/21] vmcore: check if vmcore objects satify mmap()'s page-size boundary requirement
    On Sat, 16 Mar 2013 13:02:29 +0900 HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com> wrote:

    > If there's some vmcore object that doesn't satisfy page-size boundary
    > requirement, remap_pfn_range() fails to remap it to user-space.
    >
    > Objects that posisbly don't satisfy the requirement are ELF note
    > segments only. The memory chunks corresponding to PT_LOAD entries are
    > guaranteed to satisfy page-size boundary requirement by the copy from
    > old memory to buffer in 2nd kernel done in later patch.
    >
    > This patch doesn't copy each note segment into the 2nd kernel since
    > they amount to so large in total if there are multiple CPUs. For
    > example, current maximum number of CPUs in x86_64 is 5120, where note
    > segments exceed 1MB with NT_PRSTATUS only.

    I don't really understand this. Why does the number of or size of
    note segments affect their alignment?

    > --- a/fs/proc/vmcore.c
    > +++ b/fs/proc/vmcore.c
    > @@ -38,6 +38,8 @@ static u64 vmcore_size;
    >
    > static struct proc_dir_entry *proc_vmcore = NULL;
    >
    > +static bool support_mmap_vmcore;

    This is quite regrettable. It means that on some kernels/machines,
    mmap(vmcore) simply won't work. This means that people might write
    code which works for them, but which will fail for others when deployed
    on a small number of machines.

    Can we avoid this? Why can't we just copy the notes even if there are
    a large number of them?



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