linux-kernel - Re: [PATCH v2 2/8] block,fs,mm: IO cgroup tracking for buffered write

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Message-Id: <20110323135241.4ada8334.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 23 Mar 2011 13:52:41 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Justin TerAvest <teravest@...gle.com>
Cc:	vgoyal@...hat.com, jaxboe@...ionio.com, m-ikeda@...jp.nec.com,
	ryov@...inux.co.jp, taka@...inux.co.jp, righi.andrea@...il.com,
	guijianfeng@...fujitsu.com, balbir@...ux.vnet.ibm.com,
	ctalbott@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/8] block,fs,mm: IO cgroup tracking for buffered
 write

On Tue, 22 Mar 2011 16:08:49 -0700
Justin TerAvest <teravest@...gle.com> wrote:

> +static inline void page_cgroup_set_blkio_id(struct page_cgroup *pc,
> +				unsigned long id)
> +{
> +	unsigned long old, new, prev;
> +
> +	/* pc->flags isn't lock protected, so we must cmpxchg. */
> +	WARN_ON(id >= (1UL << PAGE_TRACKING_ID_BITS));
> +	do {
> +		new = old = pc->flags;
> +		new &= (1UL << PAGE_TRACKING_ID_SHIFT) - 1;
> +		new |= (unsigned long)(id << PAGE_TRACKING_ID_SHIFT);
> +		prev = cmpxchg(&pc->flags, old, new);
> +	} while (prev != old);

How to support archs which doesn't have cmpxchg ?
At least, you need take care of compile error.

Thanks,
-Kame

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