Re: [PATCH 0/3] makedumpfile: hugepage filtering for vmcore dump

Atsushi Kumagai
2013-11-29T04:25:20Z

On 2013/11/29 12:24:45, kexec <kexec-bounces@lists.infradead.org> wrote:
> (2013/11/29 12:02), Atsushi Kumagai wrote:
> > On 2013/11/28 16:50:21, kexec <kexec-bounces@lists.infradead.org> wrote:
> >>>> ping, in case you overlooked this...
> >>>
> >>> Sorry for the delayed response, I prioritize the release of v1.5.5 now.
> >>>
> >>> Thanks for your advice, check_cyclic_buffer_overrun() should be fixed
> >>> as you said. In addition, I'm considering other way to address such case,
> >>> that is to bring the number of "overflowed pages" to the next cycle and
> >>> exclude them at the top of __exclude_unnecessary_pages() like below:
> >>>
> >>> /*
> >>> * The pages which should be excluded still remain.
> >>> */
> >>> if (remainder >= 1) {
> >>> int i;
> >>> unsigned long tmp;
> >>> for (i = 0; i < remainder; ++i) {
> >>> if (clear_bit_on_2nd_bitmap_for_kernel(pfn + i)) {
> >>> pfn_user++;
> >>> tmp++;
> >>> }
> >>> }
> >>> pfn += tmp;
> >>> remainder -= tmp;
> >>> mem_map += (tmp - 1) * SIZE(page);
> >>> continue;
> >>> }
> >>>
> >>> If this way works well, then aligning info->buf_size_cyclic will be
> >>> unnecessary.
> >>>
> >>
> >> I selected the current implementation of changing cyclic buffer size becuase
> >> I thought it was simpler than carrying over remaining filtered pages to next cycle
> >> in that there was no need to add extra code in filtering processing.
> >>
> >> I guess the reason why you think this is better now is how to detect maximum order of
> >> huge page is hard in some way, right?
> >
> > The maximum order will be gotten from HUGETLB_PAGE_ORDER or HPAGE_PMD_ORDER,
> > so I don't say it's hard. However, the carrying over method doesn't depend on
> > such kernel symbols, so I think it's robuster.
> >
>
> Then, it's better to remove check_cyclic_buffer_overrun() and rewrite part of free page
> filtering in __exclude_unnecessary_pages(). Could you do that too?

Sure, I'll modify it too.

Thanks
Atsushi Kumagai