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Date: Thu, 26 Sep 2013 21:53:16 +0200
Message-ID: <CAJfpegvvWhs+jv2J9kOQrB31PEO3kyn_sLm_e2w9YKp=y6EDhA@mail.gmail.com>
Subject: Re: [RFC] extending splice for copy offloading
From: Miklos Szeredi <miklos@szeredi.hu>
To: Zach Brown <zab@redhat.com>
Cc: "J. Bruce Fields" <bfields@fieldses.org>,
        Anna Schumaker <schumaker.anna@gmail.com>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-Fsdevel <linux-fsdevel@vger.kernel.org>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        Trond Myklebust <Trond.Myklebust@netapp.com>,
        Bryan Schumaker <bjschuma@netapp.com>,
        "Martin K. Petersen" <mkp@mkp.net>, Jens Axboe <axboe@kernel.dk>,
        Mark Fasheh <mfasheh@suse.com>, Joel Becker <jlbec@evilplan.org>,
        Eric Wong <normalperson@yhbt.net>
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Sender: linux-nfs-owner@vger.kernel.org

On Thu, Sep 26, 2013 at 9:06 PM, Zach Brown <zab@redhat.com> wrote:

>> But I'm not sure it's worth the effort; 99% of the use of this
>> interface will be copying whole files.  And for that perhaps we need a
>> different API, one which has been discussed some time ago:
>> asynchronous copyfile() returns immediately with a pollable event
>> descriptor indicating copy progress, and some way to cancel the copy.
>> And that can internally rely on ->direct_splice(), with appropriate
>> algorithms for determine the optimal  chunk size.
>
> And perhaps we don't.  Perhaps we can provide this much simpler
> data-plane interface that works well enough for most everyone and can
> avoid going down the async rat hole, yet again.

I think either buffering or async is needed to get good perforrmace
without too much complexity in the app (which is not good).  Buffering
works quite well for regular I/O, so maybe its the way to go here as
well.

Thanks,
Miklos