Subject: Re: alloc_pages_bulk()

From: Jesper Dangaard Brouer <[email-masked]>
Date: Mon, 22 Feb 2021 21:44:20 +0100

On Mon, 15 Feb 2021 12:06:09 +0000
Mel Gorman <[email-masked]> wrote:

> On Thu, Feb 11, 2021 at 04:20:31PM +0000, Chuck Lever wrote:
> > > On Feb 11, 2021, at 4:12 AM, Mel Gorman <[email-masked]> wrote:
> > > 
> > > <SNIP>
> > > 
> > > Parameters to __rmqueue_pcplist are garbage as the parameter order changed.
> > > I'm surprised it didn't blow up in a spectacular fashion. Again, this
> > > hasn't been near any testing and passing a list with high orders to
> > > free_pages_bulk() will corrupt lists too. Mostly it's a curiousity to see
> > > if there is justification for reworking the allocator to fundamentally
> > > deal in batches and then feed batches to pcp lists and the bulk allocator
> > > while leaving the normal GFP API as single page "batches". While that
> > > would be ideal, it's relatively high risk for regressions. There is still
> > > some scope for adding a basic bulk allocator before considering a major
> > > refactoring effort.
> > > 
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index f8353ea7b977..8f3fe7de2cf7 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -5892,7 +5892,7 @@ __alloc_pages_bulk_nodemask(gfp_t gfp_mask, unsigned int order,
> > > 	pcp_list = &pcp->lists[migratetype];
> > > 
> > > 	while (nr_pages) {
> > > -		page = __rmqueue_pcplist(zone, gfp_mask, migratetype,
> > > +		page = __rmqueue_pcplist(zone, migratetype, alloc_flags,
> > > 								pcp, pcp_list);
> > > 		if (!page)
> > > 			break;  
> > 
> > The NFS server is considerably more stable now. Thank you!
> >   
> 
> Thanks for testing!

I've done some testing here:
 https://github.com/xdp-project/xdp-project/blob/master/areas/mem/page_pool06_alloc_pages_bulk.org

Performance summary:
 - Before: 3,677,958 pps
 - After : 4,066,028 pps

I'll describe/show the page_pool changes tomorrow.
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer