Re: [RFC] Demand faulting for large pages

[Christoph Lameter]

On Fri, 5 Aug 2005, Andi Kleen wrote:

> > Unless I am missing something, the call to follow_hugetlb_page() in
> > get_user_pages() is just an optimization.  Removing it means
> > follow_page() will be called individually for each PAGE_SIZE page in the
> > huge page.  We can probably do better but I didn't want to cloud this
> > patch with that logic.
> 
> The problem is that get_user_pages needs to handle the case of a large
> page not yet being faulted in properly. The SLES9 implementation did
> some changes for this.
> 
> You don't change it at all, so I'm suspect it doesn't work yet.
> 
> It's a common case - think people doing raw IO on huge pages shared memory.

Seems that follow_page calls follow_huge_addr for huge pages. 
follow_huge_addr is arch specific and so we would need to verify that all 
arches do the right things if the page is not present.


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