On Mon, Aug 12, 2019 at 05:07:32PM -0700, John Hubbard wrote:
On 8/12/19 4:49 PM, Ira Weiny wrote:
quoted
On Sun, Aug 11, 2019 at 06:50:44PM -0700, john.hubbard@gmail.com wrote:
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From: John Hubbard <jhubbard@nvidia.com>
...
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diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
index 53085896d718..fdff034a8a30 100644
--- a/drivers/infiniband/core/umem_odp.c
+++ b/drivers/infiniband/core/umem_odp.c
@@ -534,7 +534,7 @@ static int ib_umem_odp_map_dma_single_page(
}
out:
- put_user_page(page);
+ vaddr_unpin_pages(&page, 1, &umem_odp->umem.vaddr_pin);
if (remove_existing_mapping) {
ib_umem_notifier_start_account(umem_odp);@@ -635,9 +635,10 @@ int ib_umem_odp_map_dma_pages(struct ib_umem_odp *umem_odp, u64 user_virt,
* complex (and doesn't gain us much performance in most use
* cases).
*/
- npages = get_user_pages_remote(owning_process, owning_mm,
+ npages = vaddr_pin_pages_remote(owning_process, owning_mm,
user_virt, gup_num_pages,
- flags, local_page_list, NULL, NULL);
+ flags, local_page_list, NULL, NULL,
+ &umem_odp->umem.vaddr_pin);
Thinking about this part of the patch... is this pin really necessary? This
code is not doing a long term pin. The page just needs a reference while we
map it into the devices page tables. Once that is done we should get notifiers
if anything changes and we can adjust. right?
OK, now it's a little interesting: the FOLL_PIN is necessary, but maybe not
FOLL_LONGTERM. Illustrating once again that it's actually necessary to allow
these flags to vary independently.
Why is PIN necessary? I think we do want all drivers to use the new
user_uaddr_vaddr_pin_user_pages() call... :-P But in this case I think a
simple "get" reference is enough to reference the page while we are using it.
If it changes after the "put/unpin" we get a fault which should handle the
change right?
The other issue I have with FOLL_PIN is what does it mean to call "...pin...()"
without FOLL_PIN?
This is another confusion of get_user_pages()... you can actually call it
without FOLL_GET... :-/ And you just don't get pages back. I've never really
dug into how (or if) you "put" them later...
And that leads to another API refinement idea: let's set FOLL_PIN within the
vaddr_pin_pages*() wrappers, and set FOLL_LONGTER in the *callers* of those
wrappers, yes?
I've thought about this before and I think any default flags should simply
define what we want follow_pages to do.
Also, the addition of vaddr_pin information creates an implicit flag which if
not there disallows any file pages from being pinned. It becomes our new
"longterm" flag. FOLL_PIN _could_ be what we should use "internally". But we
could also just use this implicit vaddr_pin flag and not add a new flag.
Finally, I struggle with converting everyone to a new call. It is more
overhead to use vaddr_pin in the call above because now the GUP code is going
to associate a file pin object with that file when in ODP we don't need that
because the pages can move around.
This overhead may be fine, not sure in this case, but I don't see everyone
wanting it.
Ira