Messages in this thread | | | From | Arnd Bergmann <> | Date | Tue, 14 Jul 2020 13:38:34 +0200 | Subject | Re: [PATCH 1/3] lib: Add a generic copy_oldmem_page() |
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On Tue, Jul 14, 2020 at 1:06 PM Christoph Hellwig <hch@infradead.org> wrote: > On Mon, Jul 13, 2020 at 03:39:17PM +0200, Arnd Bergmann wrote: > > On Mon, Jul 13, 2020 at 3:07 PM Christoph Hellwig <hch@infradead.org> wrote: > > > On Fri, Jul 10, 2020 at 08:55:42PM -0700, Palmer Dabbelt wrote: > > > > +ssize_t copy_oldmem_page(unsigned long pfn, char *buf, > > > > + size_t csize, unsigned long offset, > > > > + int userbuf) > > > > +{ > > > > + void *vaddr; > > > > + > > > > + if (!csize) > > > > + return 0; > > > > + > > > > + vaddr = memremap(__pfn_to_phys(pfn), PAGE_SIZE, MEMREMAP_WB); > > > > + if (!vaddr) > > > > + return -ENOMEM; > > > > > > Doing a memremap for every page is very inefficient. Also I don't see > > > why you'd want to even do that. All memory is in the direct mapping > > > for RISC-V. For other architecture that support highmem kmap_atomic_pfn > > > would do the job, which is what I'd use in a generic version. > > > > I would expect the 'oldmem' data to not have a 'struct page', which would > > be a problem at least for the generic implementation of kmap_atomic_pfn() > > Why do you expect it to not have a struct page?
I was under the impression that the kdump kernel only accesses a small amount of memory itself and would allocate its mem_map to fit that but not pages of that were used by the kernel it is dumping.
Arnd
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