linux-kernel - Re: [RFC V2 PATCH 2/5] cfq-iosched: preparation to handle multiple service trees

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Message-ID: <x49iqe89313.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 21 Oct 2009 11:31:52 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Corrado Zoccolo <czoccolo@...il.com>
Cc:	"Linux-Kernel" <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [RFC V2 PATCH 2/5] cfq-iosched: preparation to handle multiple service trees

Corrado Zoccolo <czoccolo@...il.com> writes:

> We embed a pointer to the service tree in each queue, to handle multiple
> service trees easily.
> Service trees are enriched with a counter.
> cfq_add_rq_rb is invoked after putting the rq in the fifo, to ensure
> that all fields in rq are properly initialized.
>
> @@ -115,6 +116,9 @@ struct cfq_queue {
>  	unsigned short ioprio_class, org_ioprio_class;
>  
>  	pid_t pid;
> +
> +	struct cfq_rb_root *service_tree;
> +	struct cfq_io_context *cic;
>  };

This change worries me.  For async queues, there is not a 1:1 mapping
between cfqq and cic.  With my forthcoming close cooperator changes, the
same will be true for sync queues.

Cheers,
Jeff
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