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Date:   Mon, 15 Feb 2021 17:10:38 +0100
From:   Jesper Dangaard Brouer <brouer@redhat.com>
To:     Mel Gorman <mgorman@techsingularity.net>
Cc:     Chuck Lever <chuck.lever@oracle.com>, Mel Gorman <mgorman@suse.de>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Jakub Kicinski <kuba@kernel.org>, brouer@redhat.com
Subject: Re: alloc_pages_bulk()
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On Mon, 15 Feb 2021 12:00:56 +0000
Mel Gorman <mgorman@techsingularity.net> wrote:

> On Thu, Feb 11, 2021 at 01:26:28PM +0100, Jesper Dangaard Brouer wrote:
[...]
> 
> > I also suggest the API can return less pages than requested. Because I
> > want to to "exit"/return if it need to go into an expensive code path
> > (like buddy allocator or compaction).  I'm assuming we have a flags to
> > give us this behavior (via gfp_flags or alloc_flags)?
> >   
> 
> The API returns the number of pages returned on a list so policies
> around how aggressive it should be allocating the requested number of
> pages could be adjusted without changing the API. Passing in policy
> requests via gfp_flags may be problematic as most (all?) bits are
> already used.

Well, I was just thinking that I would use GFP_ATOMIC instead of
GFP_KERNEL to "communicate" that I don't want this call to take too
long (like sleeping).  I'm not requesting any fancy policy :-)


For page_pool use case we use (GFP_ATOMIC | __GFP_NOWARN) flags.

static inline struct page *page_pool_dev_alloc_pages(struct page_pool *pool)
{
	gfp_t gfp = (GFP_ATOMIC | __GFP_NOWARN);

	return page_pool_alloc_pages(pool, gfp);
}

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer