On Thu, Feb 02, 2017 at 07:21:32PM +0900, AKASHI Takahiro wrote: > On Wed, Feb 01, 2017 at 04:03:54PM +0000, Mark Rutland wrote: > > Hi, > > > > On Wed, Feb 01, 2017 at 09:46:23PM +0900, AKASHI Takahiro wrote: > > > A new function, remove_pgd_mapping(), is added. > > > It allows us to unmap a specific portion of kernel mapping later as far as > > > the mapping is made using create_pgd_mapping() and unless we try to free > > > a sub-set of memory range within a section mapping. > > > > I'm not keen on adding more page table modification code. It was painful > > enough to ensure that those worked in all configurations. > > > > Why can't we reuse create_pgd_mapping()? If we pass page_mappings_only, > > and use an invalid prot (i.e. 0), what is the problem? > > As I did in v30? > (though my implementation in v30 should be improved.) Something like that. I wasn't entirely sure why we needed to change those functions so much, so I'm clearly missing something there. I'll go have another look. > > I can see that we wouldn't free/reallocate the pud or pmd entries, but > > the "wasted" memory should be small. If anything, I'd argue that it's > > preferable to keep that around so that we don't have to allocate memory > > when we need to map the crashkernel region. > > > > Is there another problem I'm missing? > > If we don't need to free unused page tables, that would make things > much simple. There are still some minor problems on the merge, but > we can sort it out. I'm not sure I follow what you mean by 'on merge' here. Could you elaborate? Thanks, Mark.
