Hello Vivek,

On Fri, 2011-08-19 at 09:48 -0400, Vivek Goyal wrote:

[snip]

quoted

quoted

Michael,

Thinking more about it. Can't we provide a arch specific version of
kmap() and kunmap() so that we create temporary mappings to copy
the pages and then these are torn off.

Isn't kmap/kunmap() used for higmem? These functions are called from
many different functions in the Linux kernel, not only for kdump. I
would assume that creating and removing mappings with these functions is
not what a caller would expect and probably would break the Linux kernel
at many other places, no?

[CCing linux-mm]

Yes it is being used for highmem pages. If arch has not defined kmap()
then generic definition is just returning page_address(page), expecting
that page will be mapped.

I was wondering that what will be broken if arch decides to extend this
to create temporary mappings for pages which are not HIGHMEM but do
not have any mapping. (Like this special case of s390).

At least we have significant additional overhead for all the other
places where kmap/kunmap is called.

I guess memory management guys can give a better answer here. As a layman,
kmap() seems to be the way to get a kernel mapping for any page frame
and if one is not already there, then arch might create one on the fly,
like we do for HIGHMEM pages. So the question is can be extend this
to also cover pages which are not highmem but do not have any mappings
on s390.

quoted

Perhaps we can finish this discussion after my vacation. I will change
my patch series that we even do not need this patch...

So how are you planning to get rid of this patch without modifying kmap(),
kunmap() implementation for s390?

I will update my patch series that we do not remove page tables for
crashkernel memory. So everything will be as on other architectures.

I hope that we can find a good solution after my vacation. Perhaps then
I have enough energy again :-)

quoted

So only two common code patches are remaining. I will send the common
code patches again and will ask Andrew Morton to integrate them in the
next merge window.The s390 patches will be integrated by Martin.

I am fine with merge of other 2 common patches. Once you repost the
series, I will ack those.

Great! I will resend the patches and contact Andrew Morton.

Thanks!

Michael

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