linux-kernel - Re: [RFC][PATCH v3 4/6] aio: Don't inherit aio ring memory at fork

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Date:	Tue, 14 Apr 2009 12:01:50 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Zach Brown <zach.brown@...cle.com>,
	Jens Axboe <jens.axboe@...cle.com>, linux-api@...r.kernel.org,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrea Arcangeli <aarcange@...hat.com>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [RFC][PATCH v3 4/6] aio: Don't inherit aio ring memory at fork

KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> writes:

> AIO folks, Am I missing anything?
>
> ===============
> Subject: [RFC][PATCH] aio: Don't inherit aio ring memory at fork
>
> Currently, mm_struct::ioctx_list member isn't copyed at fork. IOW aio context don't inherit at fork.
> but only ring memory inherited. that's strange.
>
> This patch mark DONTFORK to ring-memory too.

Well, given that clearly nobody relies on io contexts being copied to
the child, I think it's okay to make this change.  I think the current
behaviour violates the principal of least surprise, but I'm having a
hard time getting upset about that.  ;)

> In addition, This patch has good side effect. it also fix
> "get_user_pages() vs fork" problem.

Hmm, I don't follow you, here.  As I understand it, the get_user_pages
vs. fork problem has to do with the pages used for the actual I/O, not
the pages used to store the completion data.  So, could you elaborate a
bit on what you mean by the above statement?

> I think "man fork" also sould be changed. it only say
>
>        *  The child does not inherit outstanding asynchronous I/O operations from
>           its parent (aio_read(3), aio_write(3)).
> but aio_context_t (return value of io_setup(2)) also don't inherit in current implementaion.

I can certainly make that change, as I have other changes I need to push
to Michael, anyway.

Cheers,
Jeff
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