Re: [PATCH 1/4] lightnvm: add sync and close block I/O types

[Matias BjÃrling]

On 05/05/2016 11:38 AM, Javier GonzÃlez wrote:
> > On 05 May 2016, at 11:21, Matias BjÃrling <mb@xxxxxxxxxxx> wrote:
> >
> > On 05/04/2016 05:31 PM, Javier GonzÃlez wrote:
> > > Within a target, I/O requests stem from different paths, which might vary
> > > in terms of the data structures being allocated, context, etc. This
> > > might impact how the request is treated, or how memory is freed once
> > > the bio is completed.
> > >
> > > Add two different types of I/Os: (i) NVM_IOTYPE_SYNC, which indicates
> > > that the I/O is synchronous; and  (ii) NVM_IOTYPE_CLOSE_BLK, which
> > > indicates that the I/O closes the block to which all the ppas on the
> > > request belong to.
> > >
> > > Signed-off-by: Javier GonzÃlez <javier@xxxxxxxxxxxx>
> > > ---
> > >   include/linux/lightnvm.h | 2 ++
> > >   1 file changed, 2 insertions(+)
> > >
> > > diff --git a/include/linux/lightnvm.h b/include/linux/lightnvm.h
> > > index 29a6890..6c02209 100644
> > > --- a/include/linux/lightnvm.h
> > > +++ b/include/linux/lightnvm.h
> > > @@ -11,6 +11,8 @@ enum {
> > >
> > >   	NVM_IOTYPE_NONE = 0,
> > >   	NVM_IOTYPE_GC = 1,
> > > +	NVM_IOTYPE_SYNC = 2,
> > > +	NVM_IOTYPE_CLOSE_BLK = 4,
> > >   };
> > >
> > >   #define NVM_BLK_BITS (16)
> >
> > The sync should not be necessary when the read path is implemented
> > using bio_clone. Similarly for NVM_IOTYPE_CLOSE_BLK. The write
> > completion can be handled in the bio completion path.
>
> We need to know where the request comes from; we cannot do it just from
> having the bio. This is because we allocate different structures
> depending on the type of bio we send. It is not only which bio->end_io
> function we have, but which memory needs to be released. Sync is
> necessary for the read path when we have a partial bio (data both on
> write buffer and disk) that we need to fill up. Also for GC.. In this
> case, the bio is to be freed differently. In the case of close the case
> is similarly; we do not free memory on the end_io path, but on the caller.
>
> You can see how these flags are used on pblk. Maybe there is a better
> way of doing it that I could not see...

Use the bio completion path for both. For bio completion, free the data 
that is specific to the pblk flow and let the nvm_rq->end_io() 
completion path clean up the nvm_rq specific data. That will clean up 
the completion paths.

> Javier