On Wed, Jan 18, 2017 at 5:27 AM, zhong jiang <zhongjiang@xxxxxxxxxx> wrote: > 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. >> >> . >> > Addtional, if we just offline some of sectiones of dev_mappage. That will have question. > Therefore, we must offline the whole dev_mappages page that belongs to zone_device. > > is it right? please > We never online ZONE_DEVICE memory so consequently it can never be offlined. The only way to access the pages is via get_user_pages() of a DAX mapping. -- 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>