linux-kernel - Re: [ofa-general] Re: [GIT PULL] please pull ummunotify

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Message-Id: <20090915155231.DB86.A69D9226@jp.fujitsu.com>
Date:	Tue, 15 Sep 2009 16:03:04 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Roland Dreier <rdreier@...co.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Brice Goglin <Brice.Goglin@...ia.fr>,
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	general@...ts.openfabrics.org, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org
Subject: Re: [ofa-general] Re: [GIT PULL] please pull ummunotify

> 
>  > So.. What is the problem with fork? The semantics of what should
>  > happen seem natural enough to me, the PD doesn't get copied to the
>  > child, so the MR stays with the parent. COW events on the pinned
>  > region must be resolved so that the physical page stays with the
>  > process that has pinned it - the pin is logically released in the
>  > child because the MR doesn't exist because the PD doesn't exist.
> 
> This is getting away from the problem that ummunotify is solving, but
> handling a COW fault generated by the parent by doing the copy in the
> child seems like a pretty major, tricky change to make.  The child may
> have forked 100 more times in the meantime, meaning we now have to
> change 101 memory maps ... the cost of page faults goes through the roof
> probably...

Ummm...
Perhaps my first question was wrong. I'm not intent to NAK your patch.
I merely want to know your patch detail...

ok, I ask you again as another word.

 - I guess you have your MPI implementaion w/ ummunotify, right?
 - I guess you have test sevaral pattern, right?
   if so, can we see your test result?
 - I think you can explain your MPI advantage/disadvantage against
   current OpenMPI (or mpich et al).
 - I guess your patch dramatically improve MPI implementaion, but
   it's not free. it request some limitation to MPI application, right?
 - I imagine multi thread and fork. Is there another linmitaion?
 - In past discuttion, you said ummunotify user should not use
   multi threading. you also think user should not fork?



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