* Laurent Vivier (lviv...@redhat.com) wrote:
> 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())?
That's as I understand it from Andrea; and I think it does fail if you try it.
> Anyway, the code looks good:
> Reviewed-by: Laurent Vivier <lviv...@redhat.com>
Thanks.
Dave
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
