On 06/02/2017 18:32, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com> > > The kernel can't do UFFDIO_ZEROPAGE for huge pages, so we have > to allocate a temporary (always zero) page and use UFFDIO_COPYPAGE > on it. > > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com> > Reviewed-by: Juan Quintela <quint...@redhat.com> > --- > include/migration/migration.h | 1 + > migration/postcopy-ram.c | 23 +++++++++++++++++++++-- > 2 files changed, 22 insertions(+), 2 deletions(-) > > diff --git a/include/migration/migration.h b/include/migration/migration.h > index c9c1d5f..bd399fc 100644 > --- a/include/migration/migration.h > +++ b/include/migration/migration.h > @@ -108,6 +108,7 @@ struct MigrationIncomingState { > QEMUFile *to_src_file; > QemuMutex rp_mutex; /* We send replies from multiple threads */ > void *postcopy_tmp_page; > + void *postcopy_tmp_zero_page; > > QEMUBH *bh; > > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c > index a8b7fed..4c736d2 100644 > --- a/migration/postcopy-ram.c > +++ b/migration/postcopy-ram.c > @@ -324,6 +324,10 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState > *mis) > munmap(mis->postcopy_tmp_page, mis->largest_page_size); > mis->postcopy_tmp_page = NULL; > } > + if (mis->postcopy_tmp_zero_page) { > + munmap(mis->postcopy_tmp_zero_page, mis->largest_page_size); > + mis->postcopy_tmp_zero_page = NULL; > + } > trace_postcopy_ram_incoming_cleanup_exit(); > return 0; > } > @@ -593,8 +597,23 @@ int postcopy_place_page_zero(MigrationIncomingState > *mis, void *host, > return -e; > } > } else { > - /* TODO: The kernel can't use UFFDIO_ZEROPAGE for hugepages */ > - assert(0); > + /* The kernel can't use UFFDIO_ZEROPAGE for hugepages */ > + if (!mis->postcopy_tmp_zero_page) { > + mis->postcopy_tmp_zero_page = mmap(NULL, mis->largest_page_size, > + PROT_READ | PROT_WRITE, > + MAP_PRIVATE | MAP_ANONYMOUS, > + -1, 0); > + if (mis->postcopy_tmp_zero_page == MAP_FAILED) { > + int e = errno; > + mis->postcopy_tmp_zero_page = NULL; > + error_report("%s: %s mapping large zero page", > + __func__, strerror(e)); > + return -e; > + } > + memset(mis->postcopy_tmp_zero_page, '\0', > mis->largest_page_size); > + } > + return postcopy_place_page(mis, host, mis->postcopy_tmp_zero_page, > + pagesize); > }
It's sad to have to allocate 1 huge page just to zero them. Are you sure the kernel doesn't support UFFDIO_ZEROPAGE for huge page. It seems __mcopy_atomic() manages HUGETLB vma (it is called by mfill_zeropage(), called by userfaultfd_zeropage())? Anyway, the code looks good: Reviewed-by: Laurent Vivier <lviv...@redhat.com>