Hi Amit, On 2018-06-18 20:23, Amit Chandra (amichand) wrote: > > Hi experts, > > I had a question related to CMA. I have been trying to use the CMA > infra to reserve and allocate physically contiguous memory dynamically > at runtime. > > I built a custom kernel based on linux-4.14.47 to invoke the cma > initialization apis at runtime from kernel loadable module. > > I invoke cma_declare_contiguous() followed by cma_init_reserved_areas(). > > cma_declare_contiguous throws no surprises and succeeds. The issue > happens when cma_init_reserved_areas() is invoked post that. > > Here is the kernel log snippet post that call: > > Jun 15 03:30:31 ubuntu-quickstart kernel: [ 384.593218] cma: > cma_declare_contiguous(size 0x0000000200000000, base > 0x0000000000000000, limit 0x0000000000000000 alignment 0x0000000000000000) > > Jun 15 03:30:31 ubuntu-quickstart kernel: [ 384.593228] cma: Reserved > 8192 MiB at 0x0000001d4d000000 > > Jun 15 03:30:31 ubuntu-quickstart kernel: [ 384.593345] BUG: Bad page > state in process insmod pfn:1d4d000 > > Jun 15 03:30:31 ubuntu-quickstart kernel: [ 384.595758] > page:ffffefc335340000 count:0 mapcount:-127 mapping: (null) > index:0x0 > > Jun 15 03:30:31 ubuntu-quickstart kernel: [ 384.599193] flags: > 0x57fffc000000000() > > Jun 15 03:30:31 ubuntu-quickstart kernel: [ 384.600751] raw: > 057fffc000000000 0000000000000000 0000000000000000 00000000ffffff80 > > Jun 15 03:30:31 ubuntu-quickstart kernel: [ 384.603946] raw: > ffffefc335330020 ffffefc335350020 000000000000000a 0000000000000000 > > Jun 15 03:30:31 ubuntu-quickstart kernel: [ 384.607152] page dumped > because: nonzero mapcount > > I am having a hard time trying to understand why the mapcount is less > than 0 here. I figured this is happening in the call to __free_pages() > from init_cma_reserved_pageblock(). > > Any pointers here would be really helpful. If I am missing any step > for cma reservation, please do let me know. > > Thanks in advance. > CMA initialization is possible only on very early boot stage. CMA will not work as dynamic module. Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
