Hello, Vivek. 2012/12/7 Vivek Goyal <vgoyal@xxxxxxxxxx>: > On Fri, Dec 07, 2012 at 10:16:55PM +0900, JoonSoo Kim wrote: >> 2012/12/7 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>: >> > On Fri, 7 Dec 2012 01:09:27 +0900 >> > Joonsoo Kim <js1304@xxxxxxxxx> wrote: >> > >> >> I'm not sure that "7/8: makes vmlist only for kexec" is fine. >> >> Because it is related to userspace program. >> >> As far as I know, makedumpfile use kexec's output information and it only >> >> need first address of vmalloc layer. So my implementation reflect this >> >> fact, but I'm not sure. And now, I don't fully test this patchset. >> >> Basic operation work well, but I don't test kexec. So I send this >> >> patchset with 'RFC'. >> > >> > Yes, this is irritating. Perhaps Vivek or one of the other kexec >> > people could take a look at this please - if would obviously be much >> > better if we can avoid merging [patch 7/8] at all. >> >> I'm not sure, but I almost sure that [patch 7/8] have no problem. >> In kexec.c, they write an address of vmlist and offset of vm_struct's >> address field. >> It imply that user for this information doesn't have any other >> information about vm_struct, >> and they can't use other field of vm_struct. They can use *only* address field. >> So, remaining just one vm_struct for vmlist which represent first area >> of vmalloc layer >> may be safe. > > I browsed through makedumpfile source quickly. So yes it does look like > that we look at first vmlist element ->addr field to figure out where > vmalloc area is starting. > > Can we get the same information from this rb-tree of vmap_area? Is > ->va_start field communication same information as vmlist was > communicating? What's the difference between vmap_area_root and vmlist. Thanks for comment. Yes. vmap_area's va_start field represent same information as vm_struct's addr. vmap_area_root is data structure for fast searching an area. vmap_area_list is address sorted list, so we can use it like as vmlist. There is a little difference vmap_area_list and vmlist. vmlist is lack of information about some areas in vmalloc address space. For example, vm_map_ram() allocate area in vmalloc address space, but it doesn't make a link with vmlist. To provide full information about vmalloc address space, using vmap_area_list is more adequate. > 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. :) Thanks. -- 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>