* Peter Xu (pet...@redhat.com) wrote:
> On Fri, Feb 16, 2018 at 01:16:18PM +0000, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
> >
> > Cause the vhost-user client to be woken up whenever:
> > a) We place a page in postcopy mode
> > b) We get a fault and the page has already been received
> >
> > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> > ---
> > migration/postcopy-ram.c | 14 ++++++++++----
> > migration/trace-events | 1 +
> > 2 files changed, 11 insertions(+), 4 deletions(-)
> >
> > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> > index 879711968c..13561703b5 100644
> > --- a/migration/postcopy-ram.c
> > +++ b/migration/postcopy-ram.c
> > @@ -566,7 +566,11 @@ int postcopy_request_shared_page(struct PostCopyFD
> > *pcfd, RAMBlock *rb,
> >
> > trace_postcopy_request_shared_page(pcfd->idstr, qemu_ram_get_idstr(rb),
> > rb_offset);
> > - /* TODO: Check bitmap to see if we already have the page */
> > + if (ramblock_recv_bitmap_test_byte_offset(rb, aligned_rbo)) {
> > + trace_postcopy_request_shared_page_present(pcfd->idstr,
> > + qemu_ram_get_idstr(rb), rb_offset);
> > + return postcopy_wake_shared(pcfd, client_addr, rb);
> > + }
> > if (rb != mis->last_rb) {
> > mis->last_rb = rb;
> > migrate_send_rp_req_pages(mis, qemu_ram_get_idstr(rb),
> > @@ -863,7 +867,8 @@ int postcopy_place_page(MigrationIncomingState *mis,
> > void *host, void *from,
> > }
> >
> > trace_postcopy_place_page(host);
> > - return 0;
> > + return postcopy_notify_shared_wake(rb,
> > + qemu_ram_block_host_offset(rb,
> > host));
> > }
> >
> > /*
> > @@ -887,6 +892,9 @@ int postcopy_place_page_zero(MigrationIncomingState
> > *mis, void *host,
> >
> > return -e;
> > }
> > + return postcopy_notify_shared_wake(rb,
> > + qemu_ram_block_host_offset(rb,
> > +
> > host));
> > } else {
> > /* The kernel can't use UFFDIO_ZEROPAGE for hugepages */
> > if (!mis->postcopy_tmp_zero_page) {
> > @@ -906,8 +914,6 @@ int postcopy_place_page_zero(MigrationIncomingState
> > *mis, void *host,
> > return postcopy_place_page(mis, host, mis->postcopy_tmp_zero_page,
> > rb);
> > }
> > -
> > - return 0;
> > }
>
> Could there be race? E.g.:
>
> ram_load_thread page_fault_thread
> ----------------- -------------------
>
> if (recv_bitmap_set())
> wake()
> copy_page()
> recv_bitmap_set()
> wake()
> request_page()
>
> Then the last requested page may never be serviced?
The postcopy finishes when the last page is received, and thus when that
also performs the wake() (from the load thread); so that's not a
problem.
You can get the case where a page that qemu has already received, still
needs to be woken for the shared users (which is why we have the wake in
the fault_thread).
When the postcopy finishes, the client is sent a POSTCOPY_END, at which
point it closes it's userfaultfd and it should wake everything remaining
up; so any late requests shouldn't be a problem (the END is sent
before the fault-thread quits).
Dave
> Thanks,
>
> --
> Peter Xu
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
