Ingo Oeser wrote:
>
> Hi there,
>
> are huge TLB pages always physically continous in memory?
Yes.
> What does follow_hugetlb_page do exactly? I simply don't
> understand what the code does.
It allows get_user_pages() to work correctly across hugepage
regions. It walks a chunk of memory which is covered by
hugepages and installs (at *pages) the list of 4k-pages which
are covered by the hugepage. So
|--------------------------------------------------| <- hugepage
|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--| <- 4k pages
get_user_pages( ^here ^to here)
will install the spanned 4k pages into the caller's pages[]
array.
> I would like to build up a simplified get_user_pages_sgl() to
> build a scatter gather list from user space adresses.
>
> If I want to coalesce physically continous pages (if they are
> also virtually continious) anyway, can I write up a simplified
> follow_hugetlb_page_sgl() function which handles the huge page
> really as only one page?
I suggest that you restructure get_user_pages thusly:
1: Write a simplified get_user_page(). Most callers of get_user_pages()
only want a single page anyway, and don't need to concoct all those
arguments.
2: Split get_user_pages up into a pagetable walker and a callback function.
So it walks the pages, calling back to the caller's callback function
for each page with
(*callback)(struct page *page, <other stuff>, void *callerdata);
You'll need to extend follow_hugetlb_page() to take the callback
info and to perform the callbacks for its pages as well.
3: Reimplement the current get_user_pages() using the core engine from 2
(ie: write the callback for it)
4: Implement your sg engine using the walker+callback arrangement. This
way, you can do your coalescing on-the-fly, and you only take one
pass across the pages list and you do not need to know about hugepages
at all. Sure you'll do a *little* more work than you need to, but
not having that special case is nicer.
5: Fix up the ia64 follow_hugetlb_page too.
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This archive was generated by hypermail 2b29 : Thu Nov 07 2002 - 22:00:22 EST