On 1/10/22 22:31, Alex Sierra wrote:
Avoid long term pinning for Coherent device type pages. This could interfere with their own device memory manager. For now, we are just returning error for PIN_LONGTERM Coherent device type pages. Eventually, these type of pages will get migrated to system memory, once the device migration pages support is added.
Signed-off-by: Alex Sierra alex.sierra@amd.com
mm/gup.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/mm/gup.c b/mm/gup.c index 886d6148d3d0..9c8a075d862d 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1720,6 +1720,12 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages, * If we get a movable page, since we are going to be pinning * these entries, try to move them out if possible. */
if (is_device_page(head)) {WARN_ON_ONCE(is_device_private_page(head));ret = -EFAULT;goto unpin_pages;}
Wouldn't be more efficient for you failing earlier instead of after all the pages are pinned?
Filesystem DAX suffers from a somewhat similar issue[0] -- albeit it's more related to blocking FOLL_LONGTERM in gup-fast while gup-slow can still do it. Coherent devmap appears to want to block it in all gup.
On another thread Jason was suggesting about having different pgmap::flags to capture these special cases[1] instead of selecting what different pgmap types can do in various different places.
[0] https://lore.kernel.org/linux-mm/6a18179e-65f7-367d-89a9-d5162f10fef0@oracle... [1] https://lore.kernel.org/linux-mm/20211019160136.GH3686969@ziepe.ca/