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

Open Source and information security mailing list archives

Date:	Fri, 29 Nov 2013 03:02:09 +0000
From:	Atsushi Kumagai <kumagai-atsushi@....nes.nec.co.jp>
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
CC:	"bhe@...hat.com" <bhe@...hat.com>,
	"tom.vaden@...com" <tom.vaden@...com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"jingbai.ma@...com" <jingbai.ma@...com>,
	"ptesarik@...e.cz" <ptesarik@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lisa.mitchell@...com" <lisa.mitchell@...com>,
	"anderson@...hat.com" <anderson@...hat.com>,
	"ebiederm@...ssion.com" <ebiederm@...ssion.com>,
	"vgoyal@...hat.com" <vgoyal@...hat.com>
Subject: Re: [PATCH 0/3] makedumpfile: hugepage filtering for vmcore dump

On 2013/11/28 16:50:21, kexec <kexec-bounces@...ts.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.

Thanks
Atsushi Kumagai

> --
> Thanks.
> HATAYAMA, Daisuke
>
>
> _______________________________________________
> kexec mailing list
> kexec@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
>
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