Re: [PATCH] remove unnecessary PAE pgd set

[William Lee Irwin III <wli@holomorphy.com>]

William Lee Irwin III wrote:
>> I suspect this set_pgd() should go away for non-PAE also.

On Wed, Apr 30, 2003 at 08:39:04PM -0700, Dave Hansen wrote:
> Wouldn't it be analogous to the PMD set with PAE on, and necessary?
> Since processes don't share PGDs in 4G mode, the PGD entry could be
> missing in a process's pagetables after the kernel ones have been filled
> in.  That set_pgd() will be necessary to move any new entry over.

Not really; it should just fall through to the pmd "level", which as
emulated should do all the instantiation needed for non-PAE.


On Wed, Apr 30, 2003 at 08:39:04PM -0700, Dave Hansen wrote:
> - a process does a vmalloc, which eventually calls pte_alloc_kernel()
> - pte_alloc_kernel() is always called with init_mm as its mm argument
> - pte_alloc_kernel() populates init_mm PGD entries with the new pte page
> - the process goes to use its new vmalloc'd area, and faults, because
>   its pgd doesn't have the same entries.  do_page_fault():vmalloc_fault
>   brings over the necessary entries from init, and the fault is handled

Sounds like a good plan to me.


On Wed, Apr 30, 2003 at 08:39:04PM -0700, Dave Hansen wrote:
> The other option is to hold mmlist_lock and populate the entries around
> when pte_alloc_kernel() is called.  The lazy way is better because not
> every process will go looking into the vmalloc area, _and_ and new pgds
> should be copied from the init one anyway, and inherit the PTE mapping.
>  The lazy update only needs to be done for processes when their PGDs
> were allocated in the past.

Yeah, that could get ugly. Best to keep things lazy.


-- wli
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