Hello Vivek, On Fri, 2011-08-19 at 09:48 -0400, Vivek Goyal wrote: [snip] > > > 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. > > > > > 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 :-) > > 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
