On 2017/1/18 1:15, Dan Williams wrote: > On Tue, Jan 17, 2017 at 5:58 AM, zhong jiang <zhongjiang@xxxxxxxxxx> wrote: >> On 2017/1/17 18:25, Michal Hocko wrote: >>> On Mon 16-01-17 21:38:05, zhongjiang wrote: >>>> From: zhong jiang <zhongjiang@xxxxxxxxxx> >>>> >>>> At present, we skip the reservation storage by the driver for >>>> the zone_dvice. but the free pages set aside for the memmap is >>>> ignored. And since the free pages is only used as the memmap, >>>> so we can also skip the corresponding pages. >>> I have really hard time to understand what this patch does and why it >>> matters. Could you please rephrase the changelog to state, the problem, >>> how it affects users and what is the fix please? >>> >> Hi, Michal >> >> The patch maybe incorrect if free pages for memmap mapping is accouted for zone_device. >> I am just a little confusing about the implement. it maybe simple and stupid. > The patch is incorrect, the struct page initialization starts > immediately after altmap->reserve. > >> first pfn for dev_mappage come from vmem_altmap_offset, and free pages reserved for >> memmap mapping need to be accounted. I do not know the meaning. >> >> Another issue is in sparse_remove_one_section. A section belongs to zone_device is not >> always need to consider the map_offset. is it right ? From pfn_first to end , that section >> should no need to consider the map_offet. > No that's not right. devm_memremap_pages() will specify the full > physical address range that was initially hotplugged. At removal time > the first page of the memmap starts at pfn_to_page(phys_start_pfn + > map_offset). > > However, I always need to remind myself of these rules every time I > read the code, so the documentation needs improvement. The rules ensure that (reserve + free) need to less than one section size. if it is so, or we add WARNON to explicitly the limits. Thanks zhongjiang > . > -- 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>