Re: [Qemu-devel] [PATCH COLO-Frame v10 16/38] COLO: Flush PVM's cached RAM into SVM's memory

[zhanghailiang]

On 2015/11/14 0:38, Dr. David Alan Gilbert wrote:
> * zhanghailiang (address@hidden) wrote:
> > During the time of VM's running, PVM may dirty some pages, we will transfer
> > PVM's dirty pages to SVM and store them into SVM's RAM cache at next checkpoint
> > time. So, the content of SVM's RAM cache will always be some with PVM's memory
> > after checkpoint.
> >
> > Instead of flushing all content of PVM's RAM cache into SVM's MEMORY,
> > we do this in a more efficient way:
> > Only flush any page that dirtied by PVM since last checkpoint.
> > In this way, we can ensure SVM's memory same with PVM's.
> >
> > Besides, we must ensure flush RAM cache before load device state.
>
> Yes, just a couple of minor comments below; mostly OK.
>
> > Signed-off-by: zhanghailiang <address@hidden>
> > Signed-off-by: Li Zhijian <address@hidden>
> > Signed-off-by: Gonglei <address@hidden>
> > ---
> > v10: trace the number of dirty pages that be received.
> > ---
> >   include/migration/colo.h |  1 +
> >   migration/colo.c         |  2 --
> >   migration/ram.c          | 40 ++++++++++++++++++++++++++++++++++++++++
> >   trace-events             |  1 +
> >   4 files changed, 42 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/migration/colo.h b/include/migration/colo.h
> > index 8edd5f1..be2890b 100644
> > --- a/include/migration/colo.h
> > +++ b/include/migration/colo.h
> > @@ -32,4 +32,5 @@ bool migration_incoming_in_colo_state(void);
> >   /* ram cache */
> >   int colo_init_ram_cache(void);
> >   void colo_release_ram_cache(void);
> > +void colo_flush_ram_cache(void);
> >   #endif
> > diff --git a/migration/colo.c b/migration/colo.c
> > index 1339774..0efab21 100644
> > --- a/migration/colo.c
> > +++ b/migration/colo.c
> > @@ -381,8 +381,6 @@ void *colo_process_incoming_thread(void *opaque)
> >           }
> >           qemu_mutex_unlock_iothread();
> >
> > -        /* TODO: flush vm state */
> > -
> >           ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_VMSTATE_LOADED, 0);
> >           if (ret < 0) {
> >               goto out;
> > diff --git a/migration/ram.c b/migration/ram.c
> > index 70879bd..d7e0e37 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -1601,6 +1601,7 @@ static int ram_load(QEMUFile *f, void *opaque, int 
> > version_id)
> >       int flags = 0, ret = 0;
> >       static uint64_t seq_iter;
> >       int len = 0;
> > +    bool need_flush = false;
> >
> >       seq_iter++;
> >
> > @@ -1669,6 +1670,8 @@ static int ram_load(QEMUFile *f, void *opaque, int 
> > version_id)
> >                   ret = -EINVAL;
> >                   break;
> >               }
> > +
> > +            need_flush = true;
> >               ch = qemu_get_byte(f);
> >               ram_handle_compressed(host, ch, TARGET_PAGE_SIZE);
> >               break;
> > @@ -1679,6 +1682,8 @@ static int ram_load(QEMUFile *f, void *opaque, int 
> > version_id)
> >                   ret = -EINVAL;
> >                   break;
> >               }
> > +
> > +            need_flush = true;
> >               qemu_get_buffer(f, host, TARGET_PAGE_SIZE);
> >               break;
> >           case RAM_SAVE_FLAG_COMPRESS_PAGE:
> > @@ -1711,6 +1716,7 @@ static int ram_load(QEMUFile *f, void *opaque, int 
> > version_id)
> >                   ret = -EINVAL;
> >                   break;
> >               }
> > +            need_flush = true;
>
> You can probably move the 'need_flush' to the big if near the top of the loop 
> in the
> current version.

Good catch, i will fix it in next version.

> >               break;
> >           case RAM_SAVE_FLAG_EOS:
> >               /* normal exit */
> > @@ -1730,6 +1736,11 @@ static int ram_load(QEMUFile *f, void *opaque, int 
> > version_id)
> >       }
> >
> >       rcu_read_unlock();
> > +
> > +    if (!ret  && ram_cache_enable && need_flush) {
> > +        DPRINTF("Flush ram_cache\n");
>
> trace_

Got it.

> > +        colo_flush_ram_cache();
> > +    }
> >       DPRINTF("Completed load of VM with exit code %d seq iteration "
> >               "%" PRIu64 "\n", ret, seq_iter);
> >       return ret;
> > @@ -1799,6 +1810,35 @@ void colo_release_ram_cache(void)
> >       rcu_read_unlock();
> >   }
> >
> > +/*
> > + * Flush content of RAM cache into SVM's memory.
> > + * Only flush the pages that be dirtied by PVM or SVM or both.
> > + */
> > +void colo_flush_ram_cache(void)
> > +{
> > +    RAMBlock *block = NULL;
> > +    void *dst_host;
> > +    void *src_host;
> > +    ram_addr_t  offset = 0;
> > +
> > +    trace_colo_flush_ram_cache(migration_dirty_pages);
> > +    rcu_read_lock();
> > +    block = QLIST_FIRST_RCU(&ram_list.blocks);
> > +    while (block) {
> > +        offset = migration_bitmap_find_and_reset_dirty(block, offset);
>
> You'll need to rework that a little (I split that into
> migration_bitmap_find_dirty and migration_bitmap_clear_dirty)

Yes, i have rebase it in my private branch after your post-copy merged. ;)

Thanks,
zhanghailiang

> > +        if (offset >= block->used_length) {
> > +            offset = 0;
> > +            block = QLIST_NEXT_RCU(block, next);
> > +        } else {
> > +            dst_host = block->host + offset;
> > +            src_host = block->host_cache + offset;
> > +            memcpy(dst_host, src_host, TARGET_PAGE_SIZE);
> > +        }
> > +    }
> > +    rcu_read_unlock();
> > +    assert(migration_dirty_pages == 0);
> > +}
> > +
> >   static SaveVMHandlers savevm_ram_handlers = {
> >       .save_live_setup = ram_save_setup,
> >       .save_live_iterate = ram_save_iterate,
> > diff --git a/trace-events b/trace-events
> > index ee4679c..c98bc13 100644
> > --- a/trace-events
> > +++ b/trace-events
> > @@ -1232,6 +1232,7 @@ qemu_file_fclose(void) ""
> >   migration_bitmap_sync_start(void) ""
> >   migration_bitmap_sync_end(uint64_t dirty_pages) "dirty_pages %" PRIu64""
> >   migration_throttle(void) ""
> > +colo_flush_ram_cache(uint64_t dirty_pages) "dirty_pages %" PRIu64""
> >
> >   # hw/display/qxl.c
> >   disable qxl_interface_set_mm_time(int qid, uint32_t mm_time) "%d %d"
> > --
> > 1.8.3.1
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
>
> .