On 08/29/18 at 03:05pm, Kirill A. Shutemov wrote: > On Wed, Aug 29, 2018 at 10:17:54AM +0800, Baoquan He wrote: > > Vmemmap area has different base and size depending on paging mode. > > Now we just hardcode its size as 1TB in memory KASLR, it's not > > right for 5-level paging mode. > > > > Adjust it according to paging mode and use it during memory KASLR. > > > > I think 512TiB is wasteful for 5-level paging. We don't need that much. > > 1TiB limit with 4-level paging is required to fit struct pages for all > 64TiB of physical memory, assuming each struct page is 64 bytes. > > With 5-level paging the limit on physical memory is not 512-times bigger: > we cap at 52-bit physical address space. So it's just 64 times bigger and > we need only 64TiB in worst case. > > I think we can limit it further by taking into account memory_tb. Most of > machines will be fine with 1TiB there and we save few more bits from > KASLR.
Oh, do you mean to make a calculation according to the actual size of system RAM? And still taking 1TB as default, then adapt later by RAM? Then, no need to introduce VMEMMAP_SIZE_TB, this also looks good to me. Thanks Baoquan