Re: [PATCH 5/8] vmalloc: simplify vread()/vwrite()

[Nick Piggin]

On Wed, Jan 13, 2010 at 09:53:10PM +0800, Wu Fengguang wrote:
> vread()/vwrite() is only called from kcore/kmem to access one page at a time.
> So the logic can be vastly simplified.
> 
> The changes are:
> - remove the vmlist walk and rely solely on vmalloc_to_page()
> - replace the VM_IOREMAP check with (page && page_is_ram(pfn))
> - rename to vread_page()/vwrite_page()
> 
> The page_is_ram() check is necessary because kmap_atomic() is not
> designed to work with non-RAM pages.

I don't know if you can really do this. Previously vmlist_lock would be
taken, which will prevent these vm areas from being freed.

 
> Note that even for a RAM page, we don't own the page, and cannot assume
> it's a _PAGE_CACHE_WB page.

So why is this not a problem for your patch? I don't see how you handle
it.

What's the problem with the current code, exactly? I would prefer that
you continue using the same vmlist locking and checking for validating
addresses.

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