On 09/23/2016 08:42 PM, Michal Hocko wrote: >>>> no, it don't work for many special case >>>> for example, provided PMD_SIZE=2M >>>> mapping [0x1f8800, 0x208800) virtual range will be split to two ranges >>>> [0x1f8800, 0x200000) and [0x200000,0x208800) and map them separately >>>> the first range will cause dead loop >>> >>> I am not sure I see your point. How can we deadlock if _both_ addresses >>> get aligned to the page boundary and how does PMD_SIZE make any >>> difference. >>> >> i will take a example to illustrate my considerations >> provided PUD_SIZE == 1G, PMD_SIZE == 2M, PAGE_SIZE == 4K >> it is used by arm64 normally >> >> we want to map virtual range [0xffffffff_ffc08800, 0xffffffff_fffff800) by >> ioremap_page_range(),ioremap_pmd_range() is called to map the range >> finally, ioremap_pmd_range() will call >> ioremap_pte_range(pmd, 0xffffffff_ffc08800, 0xffffffff_fffe0000) and >> ioremap_pte_range(pmd, 0xffffffff_fffe0000, 0xffffffff fffff800) separately > > but those ranges are not aligned and it ioremap_page_range fix them up > to _be_ aligned then there is no problem, right? So either I am missing > something or we are talking past each other. > my complementary considerations are show below why not to round up the range start boundary to page aligned? 1, it don't remain consistent with the original logic take map [0x1800, 0x4800) as example the original logic map range [0x1000, 0x2000), but rounding up start boundary don't mapping the range [0x1000, 0x2000) 2, the rounding up start boundary maybe cause overflow, consider start boundary = 0xffffffff_fffff800 -- 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>