Re: [PATCH] 1-2-3 GB

[H. Peter Anvin]

Followup to:  <[e-mail]>
By author:    Hugh Dickins <[e-mail]>
In newsgroup: linux.dev.kernel
> 
> Usually not a problem: but if you configure for 1GB of user virtual
> and 3GB of kernel virtual, and you have more than 1GB of physical
> memory (as you normally would if chose HIGHMEM64G), then there's
> a page at physical address 0x3ffff000, directly mapped to virtual
> address 0x7ffff000.  And if that page happens to get used for the
> pmd of a process, then on exit the free_one_pgd loop wraps over
> to carry on freeing "entries" at 0x80000000, 0x80000008, ...
> A lot of pmd_ERROR messages, but eventually an entry scrapes
> through the pmd_bad test and is wrongly freed, not so good.
> 

By the way, expect user programs to fail due to lack of address space
if you only give them 1 GB of userspace.  At 1 GB of userspace there
is *no* address space which is compatible with the normal address
space map available to the user process.

I would personally vote against including that particular option.

	-hpa
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