Re: [Qemu-devel] [PATCH V10 08/20] ram/COLO: Record the dirty pages that SVM received

[Zhang Chen]

On Sat, Jul 28, 2018 at 2:51 AM, Dr. David Alan Gilbert <address@hidden
> wrote:

> * Zhang Chen (address@hidden) wrote:
> > We record the address of the dirty pages that received,
> > it will help flushing pages that cached into SVM.
> >
> > Here, it is a trick, we record dirty pages by re-using migration
> > dirty bitmap. In the later patch, we will start the dirty log
> > for SVM, just like migration, in this way, we can record both
> > the dirty pages caused by PVM and SVM, we only flush those dirty
> > pages from RAM cache while do checkpoint.
> >
> > Signed-off-by: zhanghailiang <address@hidden>
> > Reviewed-by: Dr. David Alan Gilbert <address@hidden>
> > ---
> >  migration/ram.c | 33 +++++++++++++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> >
> > diff --git a/migration/ram.c b/migration/ram.c
> > index 33ebd09d70..d1060f1337 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -3325,6 +3325,15 @@ static inline void 
> > *colo_cache_from_block_offset(RAMBlock
> *block,
> >                       __func__, block->idstr);
> >          return NULL;
> >      }
> > +
> > +    /*
> > +    * During colo checkpoint, we need bitmap of these migrated pages.
> > +    * It help us to decide which pages in ram cache should be flushed
> > +    * into VM's RAM later.
> > +    */
> > +    if (!test_and_set_bit(offset >> TARGET_PAGE_BITS, block->bmap)) {
> > +        ram_state->migration_dirty_pages++;
> > +    }
> >      return block->colo_cache + offset;
> >  }
> >
> > @@ -3555,6 +3564,24 @@ int colo_init_ram_cache(void)
> >          memcpy(block->colo_cache, block->host, block->used_length);
> >      }
> >      rcu_read_unlock();
> > +    /*
> > +    * Record the dirty pages that sent by PVM, we use this dirty bitmap
> together
> > +    * with to decide which page in cache should be flushed into SVM's
> RAM. Here
> > +    * we use the same name 'ram_bitmap' as for migration.
> > +    */
> > +    if (ram_bytes_total()) {
> > +        RAMBlock *block;
> > +
> > +        QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
>
> I think those need updating to check for 'qemu_ram_is_migratable' - it
> might be worth moving RAMBLOCK_FOREACH_MIGRATABLE.
>


OK, I will change to the " RAMBLOCK_FOREACH_MIGRATABLE " in next version.


>
> > +            unsigned long pages = block->max_length >> TARGET_PAGE_BITS;
> > +
> > +            block->bmap = bitmap_new(pages);
> > +            bitmap_set(block->bmap, 0, pages);
>
> Would it make sense to use the 'receivedmap' that was recently added
> for other uses rather than needing your own?
>

Maybe we can do this job as optimization in the future, currently we want
to make this series merged into upstream first.

Thanks
Zhang Chen


>
> Dave
>
> > +         }
> > +    }
> > +    ram_state = g_new0(RAMState, 1);
> > +    ram_state->migration_dirty_pages = 0;
> > +
> >      return 0;
> >
> >  out_locked:
> > @@ -3574,6 +3601,10 @@ void colo_release_ram_cache(void)
> >  {
> >      RAMBlock *block;
> >
> > +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> > +        g_free(block->bmap);
> > +        block->bmap = NULL;
> > +    }
> >      rcu_read_lock();
> >      QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> >          if (block->colo_cache) {
> > @@ -3582,6 +3613,8 @@ void colo_release_ram_cache(void)
> >          }
> >      }
> >      rcu_read_unlock();
> > +    g_free(ram_state);
> > +    ram_state = NULL;
> >  }
> >
> >  /**
> > --
> > 2.17.1
> >
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
>