Differece between printf and printk 4957

Peter T. Breuer The link I provided before is to a pdf file where Red Hat describe the feature. I copied this out of the .pdf, but of course omit the figures.

4GB-4GB Split Of the many new technologies included in Red Hat Enterprise Linux perhaps the most exciting is the enhanced handling of user process and kernel virtual address space in Intel x86-compatible systems. Traditionally, 32-bit x86 systems had a fixed 4GB virtual address space, which was allocated such that the kernel had 1GB and each user process 3GB (referred to as the 3-1 split). This allocation has been in use for many years, but has become restrictive as physical memory sizes have grown. With Red Hat Enterprise Linux version 3* it is possible to configure a 4-4 split, where each user process and the kernel are allocated 4GB of virtual address space. There are two important benefits to this new feature:

Ý The larger kernel virtual address space allows the system to manage more physical memory -- up to 64GB of main memory is supported by Enterprise Linux 3 on x86-compatible systems. Ý The larger user virtual address space allows applications to use approximately 30% more memory (3.7-3.8GB), improving performance for applications that take advantage of the feature. This feature is unique to Red Hat Enterprise Linux and means that x86-compatible systems can be expected to have a longer life-span and better performance.

My guess is that they just reload some MMU registers when they must and keep the same page size. But if they do not want to do that and choose to increase the page size, it may not matter all that much for systems with such large amounts of RAM.

* Note that version 3 is not the latest. Version 4 is the current release, althought version 3 will be supported for another 3 years or so.

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