Re: [PATCH 2/2] mt76: dma: add rx buffer recycle support

[Stanislaw Gruszka <sgruszka@redhat.com>]

On Wed, Dec 05, 2018 at 04:17:31PM +0100, Lorenzo Bianconi wrote:
> > On Wed, Dec 05, 2018 at 11:37:33AM +0100, Lorenzo Bianconi wrote:
> > > >
> > > > Add support for recycling rx buffers if they are not forwarded
> > > > to network stack instead of reallocate them from scratch
> > > >
> > > > Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
> > > > ---
> > > 
> > > Felix,
> > > 
> > > could you please drop this patch since it does not help to reduce pressure
> > > on page_frag_cache.
> > 
> > What is the problem ? Maybe using kmalloc() instead of page_frag_alloc()
> > could help (kmalloc has standard kmem_cache for 2048 bytes object) ?
> 
> Hi Stanislaw,
> 
> I think the only difference in using a recycle buffer with page_frag_cache is
> we are a little bit less greedy in consuming the compound page since in case of
> error we will reuse the previously allocated fragment. However we will need to
> reallocate a new compound page if we have a leftover fragment that 'locks'
> the previous compound (we have the same issue if we do not use the recycle
> buffer). Does this 'little' improvement worth a more complex code?
> Do you agree or is there something I am missing here?

I was not asking about the patch. I agree it should be droped. 

I was asking what is the problem with "pressure on page_frag_cache" and if
using kmalloc() instead of page_frag_alloc() whould be potential solution.

Regards
Stanislaw