----- Original Message ----- > On Mon, Dec 10, 2012 at 11:40:47PM +0900, JoonSoo Kim wrote: > > [..] > > > So without knowing details of both the data structures, I think if vmlist > > > is going away, then user space tools should be able to traverse vmap_area_root > > > rb tree. I am assuming it is sorted using ->addr field and we should be > > > able to get vmalloc area start from there. It will just be a matter of > > > exporting right fields to user space (instead of vmlist). > > > > There is address sorted list of vmap_area, vmap_area_list. > > So we can use it for traversing vmalloc areas if it is necessary. > > But, as I mentioned before, kexec write *just* address of vmlist and > > offset of vm_struct's address field. It imply that they don't traverse vmlist, > > because they didn't write vm_struct's next field which is needed for traversing. > > Without vm_struct's next field, they have no method for traversing. > > So, IMHO, assigning dummy vm_struct to vmlist which is implemented by [7/8] is > > a safe way to maintain a compatibility of userspace tool. :) > > Actually the design of "makedumpfile" and "crash" tool is that they know > about kernel data structures and they adopt to changes. So for major > changes they keep track of kernel version numbers and if access the > data structures accordingly. > > Currently we access first element of vmlist to determine start of vmalloc > address. True we don't have to traverse the list. > > But as you mentioned we should be able to get same information by > traversing to left most element of vmap_area_list rb tree. So I think > instead of trying to retain vmlist first element just for backward > compatibility, I will rather prefer get rid of that code completely > from kernel and let user space tool traverse rbtree. Just export > minimum needed info for traversal in user space. There's no need to traverse the rbtree. There is a vmap_area_list linked list of vmap_area structures that is also sorted by virtual address. All that makedumpfile would have to do is to access the first vmap_area in the vmap_area_list -- as opposed to the way that it does now, which is by accessing the first vm_struct in the to-be-obsoleted vmlist list. So it seems silly to keep the dummy "vmlist" around. Dave -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>