linux-kernel - Re: [PATCH 5/6] HMM: add per mirror page table.

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Message-ID: <54AE6533.2020302@mellanox.com>
Date:	Thu, 8 Jan 2015 13:08:35 +0200
From:	Haggai Eran <haggaie@...lanox.com>
To:	<j.glisse@...il.com>, <akpm@...ux-foundation.org>
CC:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	<joro@...tes.org>, Mel Gorman <mgorman@...e.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Johannes Weiner" <jweiner@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	"Rik van Riel" <riel@...hat.com>, Dave Airlie <airlied@...hat.com>,
	Brendan Conoboy <blc@...hat.com>,
	Joe Donohue <jdonohue@...hat.com>,
	Duncan Poole <dpoole@...dia.com>,
	Sherry Cheung <SCheung@...dia.com>,
	Subhash Gutti <sgutti@...dia.com>,
	John Hubbard <jhubbard@...dia.com>,
	Mark Hairgrove <mhairgrove@...dia.com>,
	Lucien Dunning <ldunning@...dia.com>,
	"Cameron Buschardt" <cabuschardt@...dia.com>,
	Arvind Gopalakrishnan <arvindg@...dia.com>,
	Shachar Raindel <raindel@...lanox.com>,
	Liran Liss <liranl@...lanox.com>,
	Roland Dreier <roland@...estorage.com>,
	Ben Sander <ben.sander@....com>,
	Greg Stoner <Greg.Stoner@....com>,
	John Bridgman <John.Bridgman@....com>,
	Michael Mantor <Michael.Mantor@....com>,
	"Paul Blinzer" <Paul.Blinzer@....com>,
	Laurent Morichetti <Laurent.Morichetti@....com>,
	Alexander Deucher <Alexander.Deucher@....com>,
	Oded Gabbay <Oded.Gabbay@....com>,
	Jérôme Glisse <jglisse@...hat.com>,
	Jatin Kumar <jakumar@...dia.com>
Subject: Re: [PATCH 5/6] HMM: add per mirror page table.

On 06/01/2015 00:44, j.glisse@...il.com wrote:
> +	/* fence_wait() - to wait on device driver fence.
> +	 *
> +	 * @fence: The device driver fence struct.
> +	 * Returns: 0 on success,-EIO on error, -EAGAIN to wait again.
> +	 *
> +	 * Called when hmm want to wait for all operations associated with a
> +	 * fence to complete (including device cache flush if the event mandate
> +	 * it).
> +	 *
> +	 * Device driver must free fence and associated resources if it returns
> +	 * something else thant -EAGAIN. On -EAGAIN the fence must not be free
> +	 * as hmm will call back again.
> +	 *
> +	 * Return error if scheduled operation failed or if need to wait again.
> +	 * -EIO Some input/output error with the device.
> +	 * -EAGAIN The fence not yet signaled, hmm reschedule waiting thread.
> +	 *
> +	 * All other return value trigger warning and are transformed to -EIO.
> +	 */
> +	int (*fence_wait)(struct hmm_fence *fence);

According to the comment, the device frees the fence struct when the
fence_wait callback returns zero or -EIO, but the code below calls
fence_unref after fence_wait on the same fence.

> +
> +	/* fence_ref() - take a reference fence structure.
> +	 *
> +	 * @fence: Fence structure hmm is referencing.
> +	 */
> +	void (*fence_ref)(struct hmm_fence *fence);

I don't see fence_ref being called anywhere in the patchset. Is it
actually needed?

> +static void hmm_device_fence_wait(struct hmm_device *device,
> +				  struct hmm_fence *fence)
> +{
> +	struct hmm_mirror *mirror;
> +	int r;
> +
> +	if (fence == NULL)
> +		return;
> +
> +	list_del_init(&fence->list);
> +	do {
> +		r = device->ops->fence_wait(fence);
> +		if (r == -EAGAIN)
> +			io_schedule();
> +	} while (r == -EAGAIN);
> +
> +	mirror = fence->mirror;
> +	device->ops->fence_unref(fence);
> +	if (r)
> +		hmm_mirror_release(mirror);
> +}
> +

Regards,
Haggai
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