linux-kernel - Re: [PATCH v6 3/5] vmcore: Introduce remap_oldmem_pfn

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Date:	Mon, 15 Jul 2013 15:44:51 +0200
From:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:	Vivek Goyal <vgoyal@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	Jan Willeke <willeke@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org
Subject: Re: [PATCH v6 3/5] vmcore: Introduce remap_oldmem_pfn_range()

On Tue, 2 Jul 2013 11:42:14 -0400
Vivek Goyal <vgoyal@...hat.com> wrote:

> On Mon, Jul 01, 2013 at 09:32:37PM +0200, Michael Holzheu wrote:
> > For zfcpdump we can't map the HSA storage because it is only available
> > via a read interface. Therefore, for the new vmcore mmap feature we have
> > introduce a new mechanism to create mappings on demand.
> > 
> > This patch introduces a new architecture function remap_oldmem_pfn_range()
> > that should be used to create mappings with remap_pfn_range() for oldmem
> > areas that can be directly mapped. For zfcpdump this is everything besides
> > of the HSA memory. For the areas that are not mapped by remap_oldmem_pfn_range()
> > a generic vmcore a new generic vmcore fault handler mmap_vmcore_fault()
> > is called.
> > 
> > This handler works as follows:
> > 
> > * Get already available or new page from page cache (find_or_create_page)
> > * Check if /proc/vmcore page is filled with data (PageUptodate)
> > * If yes:
> >   Return that page
> > * If no:
> >   Fill page using __vmcore_read(), set PageUptodate, and return page
> > 
> > Signed-off-by: Michael Holzheu <holzheu@...ux.vnet.ibm.com>
> 
> In general vmcore related changes look fine to me. I am not very familiar
> with the logic of finding pages in page cache and using page uptodate
> flag.
> 
> Hatayama, can you please review it.
> 
> Acked-by: Vivek Goyal <vgoyal@...hat.com>

Hello Vivek and Andrew,

We just realized that Hatayama's mmap patches went into v3.11-rc1. This currently
breaks s390 kdump because of the following two issues:

1) The copy_oldmem_page() is now used for copying to vmalloc memory
2) The mmap() implementation is not compatible with the current
   s390 crashkernel swap:
   See: http://marc.info/?l=kexec&m=136940802511603&w=2

The "kdump: Introduce ELF header in new memory feature" patch series will
fix both issues for s390.

There is the one small open discussion left:

http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg464856.html

But once we have finished that, would it be possible to get the
patches in 3.11?

Michael

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