From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeff Garzik <jeff@garzik.org>
Subject: Re: [PATCH 1/3 v2] chunkd: remove sendfile(2) zero-copy support
Date: Sun, 18 Jul 2010 19:23:38 -0400
Message-ID: <4C438CFA.5040703@garzik.org>
References: <20100717054616.GA9993@havoc.gtf.org> <20100717054651.GA10037@havoc.gtf.org> <4C4278EA.8000605@redhat.com> <4C4389D1.6000201@garzik.org>
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To: hail-devel@vger.kernel.org
Cc: Steven Dake <sdake@redhat.com>

On 07/18/2010 07:10 PM, Jeff Garzik wrote:
> On 07/17/2010 11:45 PM, Steven Dake wrote:
>> On 07/16/2010 10:46 PM, Jeff Garzik wrote:
>>> chunkd: remove sendfile(2) zero-copy support
>>>
>>> chunkd will be soon checksumming data in main memory. That removes
>>> the utility of a zero-copy interface which bypasses the on-heap
>>> data requirement.
>>>
>>> Signed-off-by: Jeff Garzik<jgarzik@redhat.com>
>
>> May be able to use vmsplice with sendfile (if linux is only target
>> platform). Haven't tried it myself, but the operations look interesting
>> at achieving zero copy with sockets from memory addresses.

As an aside, Project Hail -is- intended to be portable to other 
operating systems.  That said, I happily use OS-specific features if 
they have a measurable impact on our core code paths.

Another OS-specific feature I plan on using, for example, is 
sync_file_range(2) for large objects.  We can make use of the technique 
used by MythTV for streaming, which Linus describes here:

http://marc.info/?l=linux-kernel&m=127429771726842&w=2
http://marc.info/?l=linux-kernel&m=127431438118461&w=2