Re: [PATCH v5 03/12] migration/dirtyrate: Add RamlockDirtyInfo to store sampled page info

[Dr. David Alan Gilbert]

* David Edmondson (dme@dme.org) wrote:
> On Monday, 2020-08-24 at 17:14:31 +08, Chuan Zheng wrote:
> 
> > Add RamlockDirtyInfo to store sampled page info of each ramblock.
> >
> > Signed-off-by: Chuan Zheng <zhengchuan@huawei.com>
> > ---
> >  migration/dirtyrate.h | 18 ++++++++++++++++++
> >  1 file changed, 18 insertions(+)
> >
> > diff --git a/migration/dirtyrate.h b/migration/dirtyrate.h
> > index 33669b7..70000da 100644
> > --- a/migration/dirtyrate.h
> > +++ b/migration/dirtyrate.h
> > @@ -19,6 +19,11 @@
> >   */
> >  #define DIRTYRATE_DEFAULT_SAMPLE_PAGES            512
> >  
> > +/*
> > + * Record ramblock idstr
> > + */
> > +#define RAMBLOCK_INFO_MAX_LEN                     256
> > +
> >  /* Take 1s as default for calculation duration */
> >  #define DEFAULT_FETCH_DIRTYRATE_TIME_SEC          1
> >  
> > @@ -27,6 +32,19 @@ struct DirtyRateConfig {
> >      int64_t sample_period_seconds; /* time duration between two sampling */
> >  };
> >  
> > +/*
> > + * Store dirtypage info for each ramblock.
> > + */
> > +struct RamblockDirtyInfo {
> > +    char idstr[RAMBLOCK_INFO_MAX_LEN]; /* idstr for each ramblock */
> > +    uint8_t *ramblock_addr; /* base address of ramblock we measure */
> > +    uint64_t ramblock_pages; /* ramblock size in 4K-page */
> 
> It's probably a stupid question, but why not store a pointer to the
> RAMBlock rather than copying some of the details?

I think I figured that out in the last round;  this code runs as:

    rcu lock {
       calculate initial CRCs
    }

    <sleep 1 second ish>
    rcu lock {
       calculate new CRCs
    }

A RAMBlock might get deleted between the two.

Dave

       
> > +    uint64_t *sample_page_vfn; /* relative offset address for sampled page 
> > */
> > +    uint64_t sample_pages_count; /* count of sampled pages */
> > +    uint64_t sample_dirty_count; /* cout of dirty pages we measure */
> 
> "cout" -> "count"
> 
> > +    uint32_t *hash_result; /* array of hash result for sampled pages */
> > +};
> > +
> >  void *get_dirtyrate_thread(void *arg);
> >  #endif
> >  
> > -- 
> > 1.8.3.1
> 
> dme.
> -- 
> Please forgive me if I act a little strange, for I know not what I do.
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK