Re: [PATCH v3 1/3] migration: API to clear bits of guest free pages from the dirty bitmap

[Wei Wang <wei.w.wang@intel.com>]

On 03/07/2018 08:23 PM, Dr. David Alan Gilbert wrote:
> * Wei Wang (wei.w.wang@intel.com) wrote:
> > This patch adds an API to clear bits corresponding to guest free pages
> > from the dirty bitmap. Spilt the free page block if it crosses the QEMU
> > RAMBlock boundary.
> >
> > Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> > CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > CC: Juan Quintela <quintela@redhat.com>
> > CC: Michael S. Tsirkin <mst@redhat.com>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>
> > ---
> >   include/migration/misc.h |  2 ++
> >   migration/ram.c          | 20 ++++++++++++++++++++
> >   2 files changed, 22 insertions(+)
> >
> > diff --git a/include/migration/misc.h b/include/migration/misc.h
> > index 77fd4f5..fae1acf 100644
> > --- a/include/migration/misc.h
> > +++ b/include/migration/misc.h
> > @@ -14,11 +14,13 @@
> >   #ifndef MIGRATION_MISC_H
> >   #define MIGRATION_MISC_H
> >   
> > +#include "exec/cpu-common.h"
> >   #include "qemu/notify.h"
> >   
> >   /* migration/ram.c */
> >   
> >   void ram_mig_init(void);
> > +void qemu_guest_free_page_hint(void *addr, size_t len);
> >   
> >   /* migration/block.c */
> >   
> > diff --git a/migration/ram.c b/migration/ram.c
> > index 5e33e5c..769a0f6 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -2189,6 +2189,26 @@ static int ram_init_all(RAMState **rsp)
> >       return 0;
> >   }
> >   
> > +void qemu_guest_free_page_hint(void *addr, size_t len)
> > +{
> > +    RAMBlock *block;
> > +    ram_addr_t offset;
> > +    size_t used_len, start, npages;
> > +
> > +    for (used_len = len; len > 0; len -= used_len) {
> > +        block = qemu_ram_block_from_host(addr, false, &offset);
> > +        if (unlikely(offset + len > block->used_length)) {
> > +            used_len = block->used_length - offset;
> > +            addr += used_len;
> > +        }
> > +
> > +        start = offset >> TARGET_PAGE_BITS;
> > +        npages = used_len >> TARGET_PAGE_BITS;
> > +        bitmap_clear(block->bmap, start, npages);
> > +        ram_state->migration_dirty_pages -= npages;

Hi Dave,

Thanks for reviewing this patch. There will be a little more change here 
about calculating "ram_state->migration_dirty_pages" since we just 
extend this optimization to all the stages now (instead of just bulk 
stage). Please have a check more explanations at the v4 cover-letter 
ChangeLog.

Best,
Wei