Re: [Qemu-devel] [PATCH] migration/postcopy: use static PostcopyDiscardState instead of allocating it for each block

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Wei Yang (richardw.yang@linux.intel.com) wrote:
> On Fri, Jul 19, 2019 at 06:41:28PM +0100, Dr. David Alan Gilbert wrote:
> >* Wei Yang (richardw.yang@linux.intel.com) wrote:
> >> Even we need to do discard for each RAMBlock, we still can leverage the
> >> same memory space to store the information.
> >> 
> >> By doing so, we avoid memory allocation and deallocation to the system
> >> and also avoid potential failure of memory allocation which breaks the
> >> migration.
> >> 
> >> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> >> ---
> >>  migration/postcopy-ram.c | 16 +++++++---------
> >>  1 file changed, 7 insertions(+), 9 deletions(-)
> >> 
> >> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> >> index 9faacacc9e..2e6b076bb7 100644
> >> --- a/migration/postcopy-ram.c
> >> +++ b/migration/postcopy-ram.c
> >> @@ -1377,8 +1377,7 @@ void postcopy_fault_thread_notify(MigrationIncomingState *mis)
> >>   *   asking to discard individual ranges.
> >>   *
> >>   * @ms: The current migration state.
> >> - * @offset: the bitmap offset of the named RAMBlock in the migration
> >> - *   bitmap.
> >> + * @offset: the bitmap offset of the named RAMBlock in the migration bitmap.
> >>   * @name: RAMBlock that discards will operate on.
> >>   *
> >>   * returns: a new PDS.
> >> @@ -1386,13 +1385,14 @@ void postcopy_fault_thread_notify(MigrationIncomingState *mis)
> >>  PostcopyDiscardState *postcopy_discard_send_init(MigrationState *ms,
> >>                                                   const char *name)
> >>  {
> >> -    PostcopyDiscardState *res = g_malloc0(sizeof(PostcopyDiscardState));
> >> +    static PostcopyDiscardState res = {0};
> >
> >Do you think it would be better to make this a static at the top of
> >migration/postcopy-ram.c and then we could remove the pds parameters
> >from postcopy_discard_send_range and friends?
> 
> Just took a look into this one. One problem is not all its friends are in
> migration/postcopy-ram.c
> 
> For example, postcopy_chunk_hostpages_pass() is in migration/ram.c.

But doesn't that just pass teh pds back to postcopy_discard_send_range
which is in postcopy-ram ?

Dave

> Which way do you prefer?
> 
> >If there's only one pds then we don't need to pass the pointer around.
> >
> >Dave
> >
> >> -    if (res) {
> >> -        res->ramblock_name = name;
> >> -    }
> >> +    res.ramblock_name = name;
> >> +    res.cur_entry = 0;
> >> +    res.nsentwords = 0;
> >> +    res.nsentcmds = 0;
> >>  
> >> -    return res;
> >> +    return &res;
> >>  }
> >>  
> >>  /**
> >> @@ -1449,8 +1449,6 @@ void postcopy_discard_send_finish(MigrationState *ms, PostcopyDiscardState *pds)
> >>  
> >>      trace_postcopy_discard_send_finish(pds->ramblock_name, pds->nsentwords,
> >>                                         pds->nsentcmds);
> >> -
> >> -    g_free(pds);
> >>  }
> >>  
> >>  /*
> >> -- 
> >> 2.17.1
> >> 
> >--
> >Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> 
> -- 
> Wei Yang
> Help you, Help me
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK