Confirmation request about new 2.4.x. kernel limits

Hi, I would like to know whether following limits are right for kernel 2.4.x:

Max. N. of CPU: 32 (SMP)
Max. CPU speed: > 2 Ghz (up to ?)
Max. RAM size: 64 GB (any slowness accessing RAM over 4 GB
with 32 bit machines ?)
Max. file size: 1 TB (?)
Max. file system size: 2 TB (?)
Max. N. of files per FS: 2^32 (depending on max. n. of inodes ?)
Max. N. of users/groups: 2^32 (well, that's in theory, probably
practical limits, due to RAM usage,
access time, etc., are much lower).

Other upper limits, eventually compared with those of latest 2.2.x kernels, would be appreciated.

Thanks in advance for your patience.
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realistic benchmarks (unixbench) will show about 3%-6% performance degradation with use of PAE. Note that this is not "accessing RAM over 4G" but (what you probably meant) "accessing any RAM in a machine with over 4G of RAM" or even "accessing any RAM in a machine with less than 4G or RAM but running kernel capable of accessing >4G". If you really meant "accessing RAM over 4G" then you are probably talking about 36bit MTRR support which is present in recent 2.4.x kernels and works very nicely!

You can construct artificial benchmarks that will show 10% performance degradation. I haven't compared this with other PAE implementation, e.g. that of UnixWare 7.1.1+ -- this would be a very useful exercise as I vaguely remember some people claiming that Linux PAE implementation is not ideal (if it is true then it ought to be made ideal to be inline with the rest of the kernel).

Regards,
Tigran

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Max CPUs is 64 on 64 bit architectures (well you have to change NR_CPUS). I am told larger than 32 cpu ultrasparcs have booted linux already.

Anton
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Hi!

64GB on i386. I believe you can get few terabytes with ultrasparc.

Again, maybe on i386 with ext2.
Pavel

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Hi,

Actually, the 2TB limit affects all architectures, as we assume that block indexes fit into 32 bits. Blocks are passed around as unsigned longs in some cases, but even on 64-bit machines that doesn't help us as the limit still persists in the filesystem (32-bit block numbers) and device drivers (ints and 4-byte sector numbers used when generating SCSI commands).

Auditing the whole driver path to allow 64-bit block numbers, and adding the logic to generate the 5th sector address byte in the scsi command when we're doing 10-byte commands, are all possible extensions for 2.5. For now, though, the 2TB device limit is with us for all architectures and all filesystems on 2.4.

--Stephen
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