4 ms·
> RHEL used 64k page size on aarch64 for a while. I believe we have switched back to 4k. Last I checked, at least CentOS 8 (which should be the same as RHEL 8)
by cesarb 5y ago
> RHEL used 64k page size on aarch64 for a while. I believe we have switched back to 4k.
Last I checked, at least CentOS 8 (which should be the same as RHEL 8) is still using 64k pages (search at https://git.centos.org/rpms/kernel/blob/c8/f/SOURCES/kernel-aarch64.config https://git.centos.org/rpms/kernel/blob/c8/f/SOURCES/kernel-... for CONFIG_ARM64_64K_PAGES=y).
And AFAIK, to access the maximum amount of physical memory in AARCH64 (52-bit physical addresses, instead of 48 bit physical addresses), you must use 64k pages. Since RHEL is normally used on servers, it makes sense to want to be able to access huge amounts of physical memory; that's probably the true reason (or even the sole reason) RHEL uses 64k pages on AARCH64.
- Hello71 5y agoAMD64 supports only 48-bit addresses, and is still the most popular server ISA. You have: 2^48 byte You want: tebibyte 2^48 byte = 256 tebibyte 2^48 byte = (1 / 0.00390625) tebibyte how many servers do you have with more than 256 TiB of RAM?
- fulafel 5y ago56-bit support was specced and had software support already in ~2016. 48 bits is not a hard architecture limitation. see eg https://www.kernel.org/doc/html/latest/x86/x86_64/5level-paging.html https://www.kernel.org/doc/html/latest/x86/x86_64/5level-pag...
- toast0 5y agoIt's not only ram that goes in that 256 TB, memory mapped i/o uses it too. You probably don't have TB of video card RAM, but maybe some flash devices offer the whole thing memory mapped?