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@xxxxxxxxxx> >> >> 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@xxxxxxxxxx> >> Signed-off-by: Alex Sierra <alex.sierra@xxxxxxx> >> --- >> 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@xxxxxxxxxx/ > > > 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
