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Subject: Re: alloc_pages_bulk()
To:     Jesper Dangaard Brouer <brouer@redhat.com>,
        Chuck Lever <chuck.lever@oracle.com>
Cc:     "mgorman@suse.de" <mgorman@suse.de>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Mel Gorman <mgorman@techsingularity.net>
References: <2A0C36E7-8CB0-486F-A8DB-463CA28C5C5D@oracle.com>
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 <20210209113108.1ca16cfa@carbon>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <7e8efe19-94da-3f75-2380-2a54b36d5ab5@suse.cz>
Date:   Tue, 9 Feb 2021 18:27:11 +0100
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Precedence: bulk

On 2/9/21 11:31 AM, Jesper Dangaard Brouer wrote:
> On Mon, 8 Feb 2021 17:50:51 +0000
> Chuck Lever <chuck.lever@oracle.com> wrote:
> 
>> Sorry for resending. I misremembered the linux-mm address.
>> 
>> > Begin forwarded message:
>> > 
>> > [ please Cc: me, I'm not subscribed to linux-mm ]
>> > 
>> > We've been discussing how NFSD can more efficiently refill its
>> > receive buffers (currently alloc_page() in a loop; see
>> > net/sunrpc/svc_xprt.c::svc_alloc_arg()).
>> > 
> 
> It looks like you could also take advantage of bulk free in:
>  svc_free_res_pages()
> 
> I would like to use the page bulk alloc API here:
>  https://github.com/torvalds/linux/blob/master/net/core/page_pool.c#L201-L209
> 
> 
>> > 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?

Hmm the cover letter of that work says:

> The fourth patch introduces a bulk page allocator with no
> in-kernel users as an example for Jesper and others who want to
> build a page allocator for DMA-coherent pages.  It hopefully is
> relatively easy to modify this API and the one core function toget > the
semantics they require.

So it seems there were no immediate users to finalize the API?

>> > b) if not, does there exist a preferred API in 5.11 for bulk
>> > page allocation?
>> > 
>> > Many thanks for any guidance!
> 
> I have a kernel module that micro-bench the API alloc_pages_bulk() here:
>  https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/mm/bench/page_bench04_bulk.c#L97
>