Re: [PATCH] coredump_filter: add hugepage core dumping

[Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>]

Hi Kosaki-san,

KOSAKI Motohiro wrote:

> Now, hugepage's vma has VM_RESERVED flag because it cannot be swapped.
> 
> and VM_RESERVED vma isn't core dumped because its flag often be used for
> kernel internal vma (e.g. vmalloc, sound related).
> 
> So, hugepage is never dumped and it indicate hugepages's program can't be debugged easily.
> 
> In these days, demand on making use of hugepage is increasing.
> IMO, native support for coredump of hugepage is useful.
> 
> 
> I think VM_RESERVED default dumping bahavior is good,
> then I'd like to add coredump_filter mask.

> Index: b/Documentation/filesystems/proc.txt
> ===================================================================
> --- a/Documentation/filesystems/proc.txt
> +++ b/Documentation/filesystems/proc.txt
> @@ -2389,11 +2389,12 @@ will be dumped when the <pid> process is
>  of memory types. If a bit of the bitmask is set, memory segments of the
>  corresponding memory type are dumped, otherwise they are not dumped.
>  
> -The following 4 memory types are supported:
> +The following 5 memory types are supported:
>    - (bit 0) anonymous private memory
>    - (bit 1) anonymous shared memory
>    - (bit 2) file-backed private memory
>    - (bit 3) file-backed shared memory
> +  - (bit 5) hugetlb memory

Hugetlb VMAs fall also into one of the lowest 4 bit case.
If you introduce the hugetlb bit (bit 5), you'd better describe that
the hugetlb bit takes precedence over the lowest 4 bits.

Thanks,
-- 
Hidehiro Kawai
Hitachi, Systems Development Laboratory
Linux Technology Center