On Mon, Jun 03, 2013 at 03:27:18PM +0200, Michael Holzheu wrote: [..] > > If not, how would remap_pfn_range() work with HSA region when > > /proc/vmcore is mmaped()? > > I am no memory management expert, so I discussed that with Martin > Schwidefsky (s390 architecture maintainer). Perhaps something like > the following could work: > > After vmcore_mmap() is called the HSA pages are not initially mapped in > the page tables. So when user space accesses those parts > of /proc/vmcore, a fault will be generated. We implement a mechanism > that in this case the HSA is copied to a new page in the page cache and > a mapping is created for it. Since the page is allocated in the page > cache, it can be released afterwards by the kernel when we get memory > pressure. > > Our current idea for such an implementation: > > * Create new address space (struct address_space) for /proc/vmcore. > * Implement new vm_operations_struct "vmcore_mmap_ops" with > new vmcore_fault() ".fault" callback for /proc/vmcore. > * Set vma->vm_ops to vmcore_mmap_ops in mmap_vmcore(). > * The vmcore_fault() function will get a new page cache page, > copy HSA page to page cache page add it to vmcore address space. > To see how this could work, we looked into the functions > filemap_fault() in "mm/filemap.c" and relay_buf_fault() in > "kernel/relay.c". > > What do you think? I am not mm expert either but above proposal sounds reasonable to me. So remap_pfn_range() call will go in arch dependent code so that arch can decide which range can be mapped right away and which ranges will be filed in when fault happens? I am assuming that s390 will map everything except for pfn between 0 and HSA_SIZE. And regular s390 kdump will map everyting right away and will not have to rely on fault mechanism? Thanks Vivek
