linux-kernel - Question about vmsplice + SPLICE_F

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Message-ID: <ae19f8ddc770135572323dd431d0efbe3e419582.camel@linux.ibm.com>
Date:   Tue, 23 Jul 2019 17:33:24 -0300
From:   Leonardo Bras <leonardo@...ux.ibm.com>
To:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Alexander Viro <viro@...iv.linux.org.uk>
Subject: Question about vmsplice + SPLICE_F_GIFT

Hello everybody,

I am not sure if this is the right place to be asking this. If is not,
I apologize for the inconvenience. Also, please tell me where is a
better way to as these questions.

I am trying to create a basic C code to test vmsplice + SPLICE_F_GIFT
for moving memory pages between two processes without copying.

I have followed the man pages and several recipes across the web, but I
could not reproduce it yet.

Basically, I am doing:
Sending process:
- malloc + memcpy for generating pages to transfer
- vmsplice with SPLICE_F_GIFT sending over named pipe (in a loop)
Receiving process:
- Create mmaped file to receive the pages
- splice with SPLICE_F_MOVE receiving from named pipe (in a loop)

I have seen the SPLICE_F_MOVE being used on steal ops from the
'pipebuffer', but I couldn't find a way to call it from splice.

Questions: 
It does what I think it does? (reassign memory pages from a process to
another)
If so, does page gifting still works?
If so, is there a basic recipe to test it's workings?

Thank you for reading,

Leonardo Brás 

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