On 5/1/24 11:56 PM, David Hildenbrand wrote:
On 02.05.24 03:05, Alistair Popple wrote:
Jason Gunthorpe <jgg@xxxxxxxxxx> writes:
...
This doesn't make sense. IFF a blind retry is all that is needed it
should be done in the core functionality. I fear it's not that easy,
though.
+1
This migration retry weirdness is a GUP issue, it needs to be solved
in the mm not exposed to every pin_user_pages caller.
If it turns out ZONE_MOVEABLE pages can't actually be reliably moved
then it is pretty broken..
I wonder if we should remove the arbitrary retry limit in
migrate_pages() entirely for ZONE_MOVEABLE pages and just loop until
they migrate? By definition there should only be transient references on
these pages so why do we need to limit the number of retries in the
first place?
There are some weird things that still needs fixing: vmsplice() is the
example that doesn't use FOLL_LONGTERM.
Hi David!
Do you have any other call sites in mind? It sounds like one way forward
is to fix each call site...
This is an unhappy story right now: the pin_user_pages*() APIs are
significantly worse than before the "migrate pages away automatically"
upgrade, from a user point of view. Because now, the APIs fail
intermittently for callers who follow the rules--because
pin_user_pages() is not fully working yet, basically.
Other ideas, large or small, about how to approach a fix?
thanks,
--
John Hubbard
NVIDIA
