Am 2021-08-17 um 8:01 p.m. schrieb Ralph Campbell:
On 8/12/21 11:31 PM, Alex Sierra wrote:
From: Ralph Campbell rcampbell@nvidia.com
ZONE_DEVICE struct pages have an extra reference count that complicates the code for put_page() and several places in the kernel that need to check the reference count to see that a page is not being used (gup, compaction, migration, etc.). Clean up the code so the reference count doesn't need to be treated specially for ZONE_DEVICE.
v2: AS: merged this patch in linux 5.11 version
v5: AS: add condition at try_grab_page to check for the zone device type, while page ref counter is checked less/equal to zero. In case of device zone, pages ref counter are initialized to zero.
Signed-off-by: Ralph Campbell rcampbell@nvidia.com Signed-off-by: Alex Sierra alex.sierra@amd.com
arch/powerpc/kvm/book3s_hv_uvmem.c | 2 +- drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +- fs/dax.c | 4 +- include/linux/dax.h | 2 +- include/linux/memremap.h | 7 +-- include/linux/mm.h | 13 +---- lib/test_hmm.c | 2 +- mm/internal.h | 8 +++ mm/memremap.c | 68 +++++++------------------- mm/migrate.c | 5 -- mm/page_alloc.c | 3 ++ mm/swap.c | 45 ++--------------- 12 files changed, 46 insertions(+), 115 deletions(-)
I haven't seen a response to the issues I raised back at v3 of this series. https://lore.kernel.org/linux-mm/4f6dd918-d79b-1aa7-3a4c-caa67ddc29bc@nvidia...
Did I miss something?
I think part of the response was that we did more testing. Alex added support for DEVICE_GENERIC pages to test_hmm and he ran DAX tests recommended by Theodore Tso. In that testing he ran into a WARN_ON_ONCE about a zero page refcount in try_get_page. The fix is in the latest version of patch 2. But it's already obsolete because John Hubbard is about to remove that function altogether.
I think the issues you raised were more uncertainty than known bugs. It seems the fact that you can have DAX pages with 0 refcount is a feature more than a bug.
Regards, Felix