On Mar 30, 2018, at 08:31 AM, INADA Naoki songofacandy@gmail.com wrote:
Hi,
As far as I know, most amd64 and arm64 systems use only 48bit address spaces. (except [1])
[1] https://software.intel.com/sites/default/files/managed/2b/80/5-level_paging_...
It means there are some chance to compact some data structures. I point two examples below.
My question is; can we use 48bit pointer safely?
Not really, at least some CPUs can also address more memory than that. See https://lwn.net/Articles/717293/ which talks about Linux support for 57-bit virtual addresses and 52-bit physical addresses.
Ronald
Not only that, but afaik Linux could simply raise that 57bit virtual to 64bit virtual without previous warning on any version change.
On 30 March 2018 at 08:55, Ronald Oussoren ronaldoussoren@mac.com wrote:
On Mar 30, 2018, at 08:31 AM, INADA Naoki songofacandy@gmail.com wrote:
Hi,
As far as I know, most amd64 and arm64 systems use only 48bit address spaces. (except [1])
[1] https://software.intel.com/sites/default/files/managed/2b/80/5-level_paging_...
It means there are some chance to compact some data structures. I point two examples below.
My question is; can we use 48bit pointer safely?
Not really, at least some CPUs can also address more memory than that. See https://lwn.net/Articles/717293/ which talks about Linux support for 57-bit virtual addresses and 52-bit physical addresses.
Ronald
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Ronald Oussoren