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

[Dr. David Alan Gilbert]

* Zhang Chen (address@hidden) wrote:
> 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.

Sure; I think it's getting there; I don't see anything too bad in the
migration bits as is;  hopefully Jason can check the networking set
again and Markus/Eric check the QMP side of things.

Dave

> 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
> >
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK