Re: alloc_pages_bulk()

From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Chuck Lever <chuck.lever@oracle.com>,
	"mgorman@suse.de" <mgorman@suse.de>,
	Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	brouer@redhat.com, Jakub Kicinski <kuba@kernel.org>
Subject: Re: alloc_pages_bulk()
Date: Wed, 10 Feb 2021 12:41:03 +0100	[thread overview]
Message-ID: <20210210124103.56ed1e95@carbon> (raw)
In-Reply-To: <20210210084155.GA3697@techsingularity.net>

On Wed, 10 Feb 2021 08:41:55 +0000
Mel Gorman <mgorman@techsingularity.net> wrote:

> On Tue, Feb 09, 2021 at 11:31:08AM +0100, Jesper Dangaard Brouer wrote:
> > > > Neil Brown pointed me to this old thread:
> > > > 
> > > > https://lore.kernel.org/lkml/20170109163518.6001-1-mgorman@techsingularity.net/
> > > > 
> > > > We see that many of the prerequisites are in v5.11-rc, but
> > > > alloc_page_bulk() is not. I tried forward-porting 4/4 in that
> > > > series, but enough internal APIs have changed since 2017 that
> > > > the patch does not come close to applying and compiling.  
> > 
> > I forgot that this was never merged.  It is sad as Mel showed huge
> > improvement with his work.
> >   
> > > > I'm wondering:
> > > > 
> > > > a) is there a newer version of that work?
> > > >   
> > 
> > Mel, why was this work never merged upstream?
> >   
> 
> Lack of realistic consumers to drive it forward, finalise the API and
> confirm it was working as expected. It eventually died as a result. If it
> was reintroduced, it would need to be forward ported and then implement
> at least one user on top.

I guess I misunderstood you back in 2017. I though that I had presented
a clear use-case/consumer in page_pool[1].  But you wanted the code as
part of the patchset I guess.  I though, I could add it later via the
net-next tree.

It seems that Chuck now have a NFS use-case, and Hellwig also have a
use-case for DMA-iommu in __iommu_dma_alloc_pages.

The performance improvement (in above link) were really impressive!

Quote:
 "It's roughly a 50-70% reduction of allocation costs and roughly a halving of the
 overall cost of allocating/freeing batches of pages."

Who have time to revive this patchset?

I can only signup for coding the page_pool usage.
Chuck do you have time if Mel doesn't?

[1] https://github.com/torvalds/linux/blob/master/net/core/page_pool.c#L201-L209
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer