Date:	Sun, 11 Jan 2015 07:45:14 +0200
From:	Haggai Eran <haggaie@...lanox.com>
To:	Jerome Glisse <j.glisse@...il.com>
CC:	<akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>,
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	Linus Torvalds <torvalds@...ux-foundation.org>,
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Subject: Re: [PATCH 5/6] HMM: add per mirror page table.

On 10/01/2015 08:48, Jerome Glisse wrote:
> On Thu, Jan 08, 2015 at 01:05:41PM +0200, Haggai Eran wrote:
>> 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.
> 
> Yes comment is out of date, i wanted to simplify fence before readding
> it once needed (by device memory migration).
> 
>>
>>> +
>>> +	/* 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?
> 
> Not right now but the page migration to device memory use it. But i
> can remove it now.
> 
> I can respin to make comment match code but i would like to know where
> i stand on everythings else.
> 

Well, I've read patches 1 through 4, and they seemed fine, although I
still want to have a deeper look into patch 4, because the page table
code seems a little tricky. I haven't completed reading patch 5 and 6 yet.

Haggai
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